World War I

World War I (often abbreviated as WWI or WW1), also known as the First World War or the Great War, was a originating in  that lasted from 28 July 1914 to 11 November 1918. Contemporaneously described as "", it led to the mobilisation of more than 70 million, including 60 million Europeans, making it one of the largest wars in history. It is also, with an estimated nine million and seven million  , while  and the resulting  caused another 50 to 100 million deaths worldwide.

On 28 June 1914,, a ,  the Austro-Hungarian heir  in , leading to the. In response, on 23 July Austria-Hungary issued an ultimatum to. Serbia's reply failed to satisfy the Austrians, and the two moved to a war footing.

A network of interlocking alliances enlarged the crisis from a bilateral issue in the to one involving most of Europe. By July 1914, the of Europe were divided into two coalitions: the —consisting of, , and —and the  of , , and  (the Triple Alliance was only defensive in nature, allowing Italy to stay out of the war until , when it joined the  after its relations with Austria-Hungary deteriorated). Russia felt it necessary to back Serbia and, after Austria-Hungary shelled the Serbian capital of on the 28July, approved partial mobilisation. Full Russian mobilisation was announced on the evening of 30July; on the 31st, Austria-Hungary and Germany did the same, while Germany demanded Russia demobilise within twelve hours. When Russia failed to comply, Germany declared war on Russia on 1August in support of Austria-Hungary, with Austria-Hungary following suit on 6August; France ordered full mobilisation in support of Russia on 2August.

German strategy for a war on two fronts against France and Russia was to rapidly concentrate the bulk of its army in the West to defeat France within six weeks, then shift forces to the East before Russia could fully mobilise; this was later known as the. On 2August, Germany demanded, an essential element in achieving a quick victory over France. When this was refused, German forces invaded Belgium on 3August and declared war on France the same day; the Belgian government invoked the and in compliance with its obligations under this, Britain declared war on Germany on 4August. On 12 August, Britain and France also declared war on Austria-Hungary; on the 23August, sided with Britain, seizing German possessions in  and the Pacific. In November 1914, the entered the war on the side of the Central Powers, opening fronts in the, , and the. The war was fought in and drew upon each power's colonial empire as well, spreading the conflict to and across the globe. The Entente and its allies would eventually become known as the, while the grouping of Austria-Hungary, Germany and their allies would become known as the.

The German advance into France was halted at the and by the end of 1914, the  settled into a, marked by a long series of  that changed little until 1917 (the , by contrast, was marked by much greater exchanges of territory). In 1915, Italy joined the Allied Powers and opened a. joined the Central Powers in 1915 and joined the Allies in 1917, expanding the. The United States initially remained neutral, though even while neutral it became an important supplier of war materiel to the Allies. Eventually, after the sinking of American merchant ships by German submarines, the declaration by Germany that its navy would resume unrestricted attacks on neutral shipping, and that Germany was trying to incite Mexico to make war on the United States, the  on 6April 1917. Trained American forces would not begin arriving at the front in large numbers until mid-1918, but ultimately the would reach some two million troops.

Though, and joined the Allied Powers in 1916 , none of the great powers were knocked out of the war until 1918. The 1917 in Russia replaced the  with the, but continuing discontent with the cost of the war led to the , the creation of the , and the signing of the  by the new government in March 1918, ending Russia's involvement in the war. This allowed the transfer of large numbers of German troops from the East to the Western Front, resulting in the. This offensive was initially successful, but failed to score a decisive victory and exhausted the last of the German reserves. The Allies rallied and drove the Germans back in their, a continual series of attacks to which the Germans had no reply. Bulgaria was the first Central Power to sign an armistice—the on 29 September 1918. On 30 October, the Ottoman Empire capitulated, signing the. On 4November, the Austro-Hungarian empire agreed to the. With its allies defeated, at home, and the military no longer willing to fight,  abdicated on 9November and Germany signed an, effectively ending the war.

World War I was a significant turning point in the political, cultural, economic, and social climate of the world. It is considered to mark the end of the and the . The war sparked numerous. The (Britain, France, the United States, and Italy) imposed their terms on the defeated powers in a series of treaties agreed at the 1919, the most well known being the German peace treaty—the. Ultimately, as a result of the war the Austro-Hungarian, German, Ottoman, and Russian Empires ceased to exist, with numerous new states created from their remains. However, despite the conclusive Allied victory (and the creation of the during the Peace Conference, intended to prevent future wars), a  would follow just over twenty years later.

Names
The term "world war" was first used in September 1914 by German biologist and philosopher, who claimed that "there is no doubt that the course and character of the feared 'European War' ... will become the first world war in the full sense of the word," citing a wire service report in  on 20 September 1914.

Prior to, the events of 1914–1918 were generally known as the Great War or simply the World War. In October 1914, the Canadian magazine  wrote, "Some wars name themselves. This is the Great War." Contemporary Europeans also referred to it as "" or "the war to end all wars" due to their perception of its then-unparalleled scale and devastation. After World WarII began in 1939, the terms became more standard, with British Empire historians, including Canadians, favouring "The First World War" and Americans "World WarI".

Political and military alliances
For much of the 19th century, the major European powers had tried to maintain a tenuous among themselves, resulting in a complex network of political and military alliances. The biggest challenges to this were Britain's withdrawal into so-called, the and the post-1848 rise of  under. Victory in the 1866 established Prussian hegemony in Germany, while victory over France in the 1870–1871   the German states into a  under Prussian leadership.

In 1873, to isolate France and avoid a war on two fronts, Bismarck negotiated the (German: Dreikaiserbund) between Austria-Hungary, Russia and Germany. Concerned by Russia's victory in the 1877–1878 and their influence in the, the League was dissolved in 1878, with Germany and Austria-Hungary subsequently forming the 1879 ; this became the  when Italy joined in 1882.

The practical details of these alliances were limited, since their primary purpose was to ensure cooperation between the three Imperial Powers and isolate France. Attempts by Britain in 1880 to resolve colonial tensions with Russia and diplomatic moves by France led to Bismarck reforming the League in 1881. When the League finally lapsed in 1887, it was replaced by the, a secret agreement between Germany and Russia to remain neutral if either were attacked by France or Austria-Hungary.

In 1890, the new German Emperor,, forced Bismarck to retire and was persuaded not to renew the Reinsurance Treaty by the new ,. This allowed France to counteract the Triple Alliance with the of 1894 and the 1904  with Britain, while in 1907 Britain and Russia signed the. The agreements did not constitute formal alliances, but by settling long-standing colonial disputes, they made British entry into any future conflict involving France or Russia a possibility; these interlocking bilateral agreements became known as the.

Arms race
The creation of the German Reich following victory in the 1871 led to a massive increase in Germany's economic and industrial strength. Admiral and Wilhelm II, who became Emperor in 1890, sought to use that to create a Kaiserliche Marine or  to compete with Britain's  for world naval supremacy. In doing so, they were influenced by US naval strategist, who argued possession of a was vital for global power projection; Tirpitz translated his books into German and Wilhelm made them required reading. However, it was also driven by Wilhelm's admiration of the Royal Navy and desire to outdo it.

This resulted in the but the launch of HMS Dreadnought (1906) in 1906 gave the Royal Navy a technological advantage over its German rival, which they never lost. Ultimately, the race diverted huge resources to creating a German navy large enough to antagonise Britain, but not defeat it. In 1911, Chancellor acknowledged defeat, leading to the Rüstungswende or ‘armaments turning point', when Germany switched expenditure from the navy to the army.

This was driven by Russia's recovery from the, specifically increased investment post 1908 in railways and infrastructure in its western border regions. Germany and Austria-Hungary relied on faster mobilisation to compensate for fewer numbers; it was concern at the closing of this gap that led to the end of the naval race, rather than a reduction in tension elsewhere. When Germany expanded its standing army by 170,000 men in 1913, France extended compulsory military service from two to three years; similar measures taken by the and Italy led to increased expenditure by the  and Austria-Hungary. Absolute figures are hard to calculate, due to differences in categorising expenditure, while they often omit civilian infrastructure projects with a military use, such as railways. However, from 1908 to 1913, defence spending by the six major European powers increased by over 50% in real terms.

Conflicts in the Balkans
In October 1908, Austria-Hungary precipitated the of 1908–1909 by officially annexing the former Ottoman territory of, which it  since 1878. This angered the and its patron, the  and. Russian political manoeuvring in the region destabilised peace accords that were already fracturing in the Balkans, which came to be known as the "".

In 1912 and 1913, the was fought between the  and the fracturing Ottoman Empire. The resulting further shrank the Ottoman Empire, creating an independent n state while enlarging the territorial holdings of Bulgaria, Serbia,, and. When Bulgaria attacked Serbia and Greece on 16 June 1913, it sparked the 33-day, by the end of which it lost most of to Serbia and Greece, and  to Romania, further destabilising the region. The were able to keep these Balkan conflicts contained, but the next one would spread throughout Europe and beyond.

Sarajevo assassination
On 28 June 1914,, heir presumptive to the , visited the capital,. A group of six assassins (,, , , , and ) from the group , supplied with arms by the Serbian , gathered on the street where the Archduke's motorcade was to pass, with the intention of assassinating him. The political objective of the assassination was to break off Austria-Hungary's South Slav provinces, which Austria-Hungary had annexed from the Ottoman Empire, so they could be combined into a Yugoslavia.

Čabrinović threw a at the car, but missed. Some nearby were injured by the blast, but Ferdinand's convoy carried on. The other assassins failed to act as the cars drove past them.

About an hour later, when Ferdinand was returning from a visit at the Sarajevo Hospital with those wounded in the assassination attempt, the convoy took a wrong turn into a street where, by coincidence, Princip stood. With a pistol, Princip shot and killed Ferdinand and his wife. Although they were reportedly not personally close, the Emperor was profoundly shocked and upset. The reaction among the people in Austria, however, was mild, almost indifferent. As historian later wrote, "the event almost failed to make any impression whatsoever. On Sunday and Monday (28 and 29 June), the crowds in  listened to music and drank wine, as if nothing had happened." Nevertheless, the political effect of the murder of the heir to the throne was significant, and was described by historian on the BBC Radio4 series Month of Madness as a ", a terrorist event charged with historic meaning, transforming the political chemistry in Vienna."

Expansion of violence in Bosnia and Herzegovina
The Austro-Hungarian authorities encouraged the subsequent, in which and  killed two  and damaged numerous Serb-owned buildings. Violent actions against ethnic Serbs were also organised outside Sarajevo, in other cities in Austro-Hungarian-controlled Bosnia and Herzegovina, Croatia and Slovenia. Austro-Hungarian authorities in Bosnia and Herzegovina imprisoned and extradited approximately 5,500 prominent Serbs, 700 to 2,200 of whom died in prison. A further 460 Serbs were sentenced to death. A predominantly Bosniak special militia known as the  was established and carried out the persecution of Serbs.

July Crisis
The assassination led to a month of diplomatic manoeuvring between Austria-Hungary, Germany, Russia, France and Britain, called the. Austria-Hungary correctly believed that Serbian officials (especially the officers of the Black Hand) were involved in the plot to murder the Archduke, and wanted to finally end Serbian interference in Bosnia. On 23July, Austria-Hungary delivered to Serbia the, a series of ten demands that were made intentionally unacceptable, in an effort to provoke a war with Serbia. Serbia decreed general mobilisation on 25July. Serbia accepted all the terms of the ultimatum except for article six, which demanded that Austrian delegates be allowed in Serbia for the purpose of participation in the investigation into the assassination. Following this, Austria broke off diplomatic relations with Serbia and, the next day, ordered a partial mobilisation. Finally, on 28 July 1914, a month after the assassination, Austria-Hungary declared war on Serbia.

On 25July, Russia, in support of Serbia, declared partial mobilisation against Austria-Hungary. On 30July, Russia ordered general mobilisation. German Chancellor Bethmann-Hollweg waited until the 31st for an appropriate response, when Germany declared Erklärung des Kriegszustandes, or "Statement on the war status". Kaiser Wilhelm II asked his cousin, Tsar, to suspend the Russian general mobilisation. When he refused, Germany issued an ultimatum demanding its mobilisation be stopped, and a commitment not to support Serbia. Another was sent to France, asking her not to support Russia if it were to come to the defence of Serbia. On 1August, after the Russian response, Germany mobilised and declared war on Russia. This also led to the general mobilisation in Austria-Hungary on 4August.

The German government issued demands to France that it remain neutral as they had to decide which deployment plan to implement, it being extremely difficult to change the deployment whilst it was underway. The modified German, Aufmarsch II West, would deploy 80% of the army in the west, while Aufmarsch I Ost and Aufmarsch II Ost would deploy 60% in the west and 40% in the east. The French did not respond, but sent a mixed message by ordering their troops to withdraw 10 km from the border to avoid any incidents, and at the same time ordered the mobilisation of their reserves. Germany responded by mobilising its own reserves and implementing Aufmarsch II West.

On 1 August, Wilhelm ordered General to "march the whole of the... army to the East" after being wrongly informed that the British would remain neutral if France was not attacked. Moltke told the Kaiser that attempting to redeploy a million men was unthinkable, and that making it possible for the French to attack the Germans "in the rear" would prove disastrous. Yet Wilhelm insisted that the German army should not march into until he received a telegram sent by his cousin, who made it clear that there had been a misunderstanding. Eventually the Kaiser told Moltke, "Now you can do what you want."

On 2 August,, and on 3August declared war on France; on the same day, they sent the Belgian government an ultimatum demanding unimpeded right of way through any part of Belgium, which was refused. Early on the morning of 4August, the Germans invaded; ordered his military to resist and called for assistance under the. Britain demanded Germany comply with the Treaty and respect Belgian neutrality; it declared war on Germany at 19:00 UTC on 4August 1914 (effective from 23:00), following an "unsatisfactory reply".

Confusion among the Central Powers
The strategy of the Central Powers suffered from miscommunication. Germany had promised to support Austria-Hungary's invasion of Serbia, but interpretations of what this meant differed. Previously tested deployment plans had been replaced early in 1914, but those had never been tested in exercises. Austro-Hungarian leaders believed Germany would cover its northern flank against Russia. Germany, however, envisioned Austria-Hungary directing most of its troops against Russia, while Germany dealt with France. This confusion forced the to divide its forces between the Russian and Serbian fronts.

Serbian campaign
Austria invaded and fought the Serbian army at the and  beginning on 12 August. Over the next two weeks, Austrian attacks were thrown back with heavy losses, which marked the first major Allied victories of the war and dashed Austro-Hungarian hopes of a swift victory. As a result, Austria had to keep sizeable forces on the Serbian front, weakening its efforts against Russia. Serbia's defeat of the Austro-Hungarian invasion of 1914 has been called one of the major upset victories of the twentieth century. The campaign saw the very first use of by the Serbian army in autumn of 1915 and  in the spring of 1915 after an Austrian plane was shot down with  fire.

German Offensive in Belgium and France
When the war began, the placed 80% of the army in the West, with the remainder acting as a screening force in the East. The plan was to quickly knock France out of the war, then redeploy to the East and do the same to Russia.

The German offensive in the West was officially titled Aufmarsch II West, but is better known as the Schlieffen Plan, after its original creator. deliberately kept the German left (i.e. its positions in ) weak to lure the French into attacking there, while the majority were allocated to the German right, so as to sweep through Belgium, encircle Paris and trap the French armies against the Swiss border (the French charged into Alsace-Lorraine on the outbreak of war as envisaged by their, thus actually aiding this strategy). However, Schlieffen's successor Moltke grew concerned that the French might push too hard on his left flank. As such, as the German Army increased in size in the years leading up to the war, he changed the allocation of forces between the German right and left wings from 85:15 to 70:30. Ultimately, Moltke's changes meant insufficient forces to achieve decisive success and thus unrealistic goals and timings.

The initial German advance in the West was very successful: by the end of August the Allied left, which included the (BEF), was in ; French casualties in the first month exceeded 260,000, including 27,000 killed on 22 August during the. German planning provided broad strategic instructions, while allowing army commanders considerable freedom in carrying them out at the front; this worked well in 1866 and 1870 but in 1914, used this freedom to disobey orders, opening a gap between the German armies as they closed on Paris. The French and British exploited this gap to halt the German advance east of Paris at the from 5to 12 September and push the German forces back some 50 km.

In 1911, the Russian had agreed with the French to attack Germany within 15 days of mobilisation; this was unrealistic and the two Russian armies that entered  on 17 August did so without many of their support elements. The was effectively destroyed at the  on 26–30 August but the Russian advance caused the Germans to re-route their  from France to East Prussia, a factor in Allied victory on the Marne.

By the end of 1914, German troops held strong defensive positions inside France, controlled the bulk of France's domestic coalfields and had inflicted 230,000 more casualties than it lost itself. However, communications problems and questionable command decisions cost Germany the chance of a decisive outcome while it had failed to achieve the primary objective of avoiding a long, two-front war. This amounted to a strategic defeat; shortly after the Marne, told an American reporter; "We have lost the war. It will go on for a long time but lost it is already."

Asia and the Pacific
New Zealand  (later Western Samoa) on 30 August 1914. On 11 September, the landed on the island of  (later New Britain), which formed part of. On 28 October, the German cruiser SMS Emden (1908) sank the in the. Japan seized Germany's Micronesian colonies and, after the, the German coaling port of on the Chinese  peninsula. As Vienna refused to withdraw the Austro-Hungarian cruiser SMS Kaiserin Elisabeth from Tsingtao, Japan declared war not only on Germany, but also on Austria-Hungary; the ship participated in the defence of Tsingtao where it was sunk in November 1914. Within a few months, the Allied forces had seized all the German territories in the Pacific; only isolated commerce raiders and a few holdouts in New Guinea remained.

African campaigns
Some of the first clashes of the war involved British, French, and German colonial forces in Africa. On 6–7 August, French and British troops invaded the German protectorate of and. On 10 August, German forces in attacked South Africa; sporadic and fierce fighting continued for the rest of the war. The German colonial forces in, led by Colonel , fought a campaign during World WarI and only surrendered two weeks after the armistice took effect in Europe.

Indian support for the Allies
Germany attempted to use Indian nationalism and pan-Islamism to its advantage,, and that urged Afghanistan to join the war on the side of Central Powers. However, contrary to British fears of a revolt in India, the outbreak of the war saw an unprecedented outpouring of loyalty and goodwill towards Britain. Indian political leaders from the and other groups were eager to support the British war effort, since they believed that strong support for the war effort would further the cause of. The in fact outnumbered the British Army at the beginning of the war; about 1.3 million Indian soldiers and labourers served in Europe, Africa, and the Middle East, while the central government and the s sent large supplies of food, money, and ammunition. In all, 140,000 men served on the Western Front and nearly 700,000 in the Middle East. Casualties of Indian soldiers totalled 47,746 killed and 65,126 wounded during World WarI. The suffering engendered by the war, as well as the failure of the British government to grant self-government to India after the end of hostilities, bred disillusionment and fuelled that would be led by  and others.

Trench warfare begins
Military tactics developed before World War I failed to keep pace with advances in technology and had become obsolete. These advances had allowed the creation of strong defensive systems, which out-of-date military tactics could not break through for most of the war. was a significant hindrance to massed infantry advances, while, vastly more lethal than in the 1870s, coupled with s, made crossing open ground extremely difficult. Commanders on both sides failed to develop tactics for positions without heavy casualties. In time, however, technology began to produce new offensive weapons, such as and the.

After the (5–12 September 1914), Allied and German forces unsuccessfully tried to outflank each other, a series of manoeuvres later known as the "". By the end of 1914, the opposing forces were left confronting each other along an uninterrupted line of entrenched positions from to Belgium's North Sea coast. Since the Germans were able to choose where to stand, they normally had the advantage of the high ground; in addition, their trenches tended to be better built, since Anglo-French trenches were initially intended as "temporary," preparatory to breaking the German defences.

Both sides tried to break the stalemate using scientific and technological advances. On 22 April 1915, at the, the Germans (violating the ) used gas for the first time on the Western Front. Several types of gas soon became widely used by both sides, and though it never proved a decisive, battle-winning weapon, poison gas became one of the most-feared and best-remembered horrors of the war. Tanks were developed by Britain and France and were first used in combat by the British during the (part of the Battle of the Somme) on 15 September 1916, with only partial success. However, their effectiveness would grow as the war progressed; the Allies built tanks in large numbers, whilst the Germans employed only a few of their own design, supplemented by captured Allied tanks.

Continuation of trench warfare
Neither side proved able to deliver a decisive blow for the next two years. Throughout 1915–17, the British Empire and France suffered more casualties than Germany, because of both the strategic and tactical stances chosen by the sides. Strategically, while the Germans mounted only one major offensive, the Allies made several attempts to break through the German lines.

In February 1916 the Germans attacked French defensive positions at the, lasting until December 1916. The Germans made initial gains, before French counter-attacks returned matters to near their starting point. Casualties were greater for the French, but the Germans bled heavily as well, with anywhere from 700,000 to 975,000 casualties suffered between the two combatants. Verdun became a symbol of French determination and self-sacrifice.

The was an Anglo-French offensive of July to November 1916. The of the offensive (1 July 1916) was the bloodiest day in the history of the, suffering 57,470 casualties, including 19,240 dead. The entire Somme offensive cost the British Army some 420,000 casualties. The French suffered another estimated 200,000 casualties and the Germans an estimated 500,000. Gun fire was not the only factor taking lives; the diseases that emerged in the trenches were a major killer on both sides. The living conditions made it so that countless diseases and infections occurred, such as, shell shock, blindness/burns from mustard gas, lice, trench fever, cooties (body lice) and the 'Spanish Flu'.

To maintain morale, wartime censors minimised early reports of widespread illness and mortality in Germany, the United Kingdom, France, and the United States. Papers were free to report the epidemic's effects in neutral Spain (such as the grave illness of ). This created a false impression of Spain as especially hard hit, thereby giving rise to the pandemic's nickname, "Spanish Flu".

Protracted action at Verdun throughout 1916, combined with the bloodletting at the Somme, brought the exhausted French army to the brink of collapse. Futile attempts using came at a high price for both the British and the French and led to the widespread, after the failure of the costly  of April–May 1917. The concurrent British was more limited in scope, and more successful, although ultimately of little strategic value. A smaller part of the Arras offensive, the capture of by the, became highly significant to that country: the idea that Canada's national identity was born out of the battle is an opinion widely held in military and general histories of Canada.

The last large-scale offensive of this period was a British attack (with French support) at (July–November 1917). This offensive opened with great promise for the Allies, before bogging down in the October mud. Casualties, though disputed, were roughly equal, at some 200,000–400,000 per side.

The years of trench warfare on the Western front achieved no major exchanges of territory and, as a result, are often thought of as static and unchanging. However, throughout this period, British, French, and German to meet new battlefield challenges.

Naval war
At the start of the war, the German Empire had s scattered across the globe, some of which were subsequently used to attack Allied. The British Royal Navy systematically hunted them down, though not without some embarrassment from its inability to protect Allied shipping. Before the beginning of the war, it was widely understood that Britain held the position of strongest, most influential navy in the world. The publishing of the book  by Alfred Thayer Mahan in 1890 was intended to encourage the United States to increase their naval power. Instead, this book made it to Germany and inspired its readers to try to over-power the British Royal Navy. For example, the German detached light cruiser SMS Emden, part of the stationed at Qingdao, seized or destroyed 15 merchantmen, as well as sinking a Russian cruiser and a French destroyer. However, most of the —consisting of the armoured cruisers SMS Scharnhorst and SMS Gneisenau, light cruisers SMS Nürnberg (1906) and SMS Leipzig (1905) and two transport ships—did not have orders to raid shipping and was instead underway to Germany when it met British warships. The German flotilla and SMS Dresden (1907) sank two armoured cruisers at the, but was virtually destroyed at the in December 1914, with only Dresden and a few auxiliaries escaping, but after the  these too had been destroyed or interned.

Soon after the outbreak of hostilities, Britain began a naval. The strategy proved effective, cutting off vital military and civilian supplies, although this blockade violated accepted international law codified by several international agreements of the past two centuries. Britain mined international waters to prevent any ships from entering entire sections of ocean, causing danger to even neutral ships. Since there was limited response to this tactic of the British, Germany expected a similar response to its unrestricted submarine warfare.

The (German: Skagerrakschlacht, or "Battle of the ") in May/June 1916 developed into the largest naval battle of the war. It was the only full-scale clash of battleships during the war, and one of the largest in history. The Kaiserliche Marine's, commanded by Vice Admiral , fought the Royal Navy's , led by Admiral Sir. The engagement was a stand off, as the Germans were outmanoeuvred by the larger British fleet, but managed to escape and inflicted more damage to the British fleet than they received. Strategically, however, the British asserted their control of the sea, and the bulk of the German surface fleet remained confined to port for the duration of the war.

German s attempted to cut the supply lines between North America and Britain. The nature of meant that attacks often came without warning, giving the crews of the merchant ships little hope of survival. The United States launched a protest, and Germany changed its rules of engagement. After the sinking of the passenger ship in 1915, Germany promised not to target passenger liners, while Britain armed its merchant ships, placing them beyond the protection of the "", which demanded warning and movement of crews to "a place of safety" (a standard that lifeboats did not meet). Finally, in early 1917, Germany adopted a policy of, realising the Americans would eventually enter the war. Germany sought to strangle Allied s before the United States could transport a large army overseas, but after initial successes eventually failed to do so.

The U-boat threat lessened in 1917, when merchant ships began travelling in, escorted by s. This tactic made it difficult for U-boats to find targets, which significantly lessened losses; after the and s were introduced, accompanying destroyers could attack a submerged submarine with some hope of success. Convoys slowed the flow of supplies, since ships had to wait as convoys were assembled. The solution to the delays was an extensive program of building new freighters. Troopships were too fast for the submarines and did not travel the North Atlantic in convoys. The U-boats had sunk more than 5,000 Allied ships, at a cost of 199 submarines.

World War I also saw the first use of s in combat, with HMS Furious (47) launching s in a successful raid against the hangars at  in July 1918, as well as s for antisubmarine patrol.

War in the Balkans
Faced with Russia in the east, Austria-Hungary could spare only one-third of its army to attack Serbia. After suffering heavy losses, the Austrians briefly occupied the Serbian capital,. A Serbian counter-attack in the Battle of Kolubara succeeded in driving them from the country by the end of 1914. For the first ten months of 1915, Austria-Hungary used most of its military reserves to fight Italy. German and Austro-Hungarian diplomats, however, scored a coup by persuading Bulgaria to join the attack on Serbia. The Austro-Hungarian provinces of, Croatia and provided troops for Austria-Hungary in the fight with Serbia, Russia and Italy. Montenegro allied itself with Serbia.

Bulgaria declared war on Serbia on 12 October 1915 and joined in the attack by the Austro-Hungarian army under Mackensen's army of 250,000 that was already underway. Serbia was conquered in a little more than a month, as the Central Powers, now including Bulgaria, sent in 600,000 troops total. The Serbian army, fighting on two fronts and facing certain defeat, retreated into northern. The Serbs suffered defeat in the. Montenegro covered the Serbian retreat towards the Adriatic coast in the in 6–7 January 1916, but ultimately the Austrians also conquered Montenegro. The surviving Serbian soldiers were evacuated by ship to Greece. After conquest, Serbia was divided between Austro-Hungary and Bulgaria.

In late 1915, a Franco-British force landed at in Greece to offer assistance and to pressure its government to declare war against the Central Powers. However, the pro-German dismissed the pro-Allied government of  before the Allied expeditionary force arrived. The friction between the King of Greece and the Allies continued to accumulate with the, which effectively divided Greece between regions still loyal to the king and the new provisional government of Venizelos in Salonica. After intense negotiations and an armed confrontation in between Allied and royalist forces (an incident known as ), the King of Greece resigned and his second son  took his place; Greece officially joined the war on the side of the Allies in June 1917.

The Macedonian Front was initially mostly static. French and Serbian forces retook limited areas of Macedonia by recapturing on 19 November 1916 following the costly, which brought stabilisation of the front.

Serbian and French troops finally made a breakthrough in September 1918 in the, after most of the German and Austro-Hungarian troops had been withdrawn. The Bulgarians were defeated at the, and by 25 September British and French troops had crossed the border into Bulgaria proper as the Bulgarian army collapsed. Bulgaria capitulated four days later, on 29 September 1918. The German high command responded by despatching troops to hold the line, but these forces were far too weak to reestablish a front.

The disappearance of the Macedonian Front meant that the road to and Vienna was now opened to Allied forces. Hindenburg and Ludendorff concluded that the strategic and operational balance had now shifted decidedly against the and, a day after the Bulgarian collapse, insisted on an immediate peace settlement.

Ottoman Empire
The Ottomans threatened Russia's territories and Britain's communications with India via the. As the conflict progressed, the Ottoman Empire took advantage of the European powers' preoccupation with the war and conducted large-scale ethnic cleansing of the indigenous, , and Christian populations, known as the , , and.

The British and French opened overseas fronts with the (1915) and s (1914). In Gallipoli, the Ottoman Empire successfully repelled the British, French, and (ANZACs). In, by contrast, after the defeat of the British defenders in the by the Ottomans (1915–16), British Imperial forces reorganised and captured  in March 1917. The British were aided in Mesopotamia by local Arab and Assyrian tribesmen, while the Ottomans employed local Kurdish and Turcoman tribes.

Further to the west, the Suez Canal was defended from Ottoman attacks in 1915 and 1916; in August, a German and Ottoman force was defeated at the by the  and the. Following this victory, an advanced across the, pushing Ottoman forces back in the  in December and the  on the border between the Egyptian  and Ottoman Palestine in January 1917.

Russian armies generally had success in the Caucasus. , supreme commander of the Ottoman armed forces, was ambitious and dreamed of re-conquering central Asia and areas that had been lost to Russia previously. He was, however, a poor commander. He launched an offensive against the Russians in the Caucasus in December 1914 with 100,000 troops, insisting on a frontal attack against mountainous Russian positions in winter. He lost 86% of his force at the.

The Ottoman Empire, with German support, invaded (modern ) in December 1914 in an effort to cut off British and Russian access to s around  near the. Persia, ostensibly neutral, had long been under the spheres of British and Russian influence. The Ottomans and Germans were aided by and  forces, together with a large number of major Iranian tribes, such as the, s, s, and , while the Russians and British had the support of Armenian and Assyrian forces. The was to last until 1918 and end in failure for the Ottomans and their allies. However, the Russian withdrawal from the war in 1917 led to Armenian and Assyrian forces, who had hitherto inflicted a series of defeats upon the forces of the Ottomans and their allies, being cut off from supply lines, outnumbered, outgunned and isolated, forcing them to fight and flee towards British lines in northern Mesopotamia.

General, the Russian commander from 1915 to 1916, drove the Turks out of most of the southern Caucasus with a string of victories. In 1917, Russian assumed command of the Caucasus front. Nicholas planned a railway from to the conquered territories, so that fresh supplies could be brought up for a new offensive in 1917. However, in March 1917 (February in the pre-revolutionary Russian calendar), the Tsar abdicated in the course of the, and the began to fall apart.

The, instigated by the Arab bureau of the British , started June 1916 with the , led by of , and ended with the Ottoman surrender of Damascus. , the Ottoman commander of, resisted for more than two and half years during the before surrendering in January 1919.

The tribe, along the border of Italian Libya and British Egypt, incited and armed by the Turks, waged a small-scale guerrilla war against Allied troops. The British were forced to dispatch 12,000 troops to oppose them in the. Their rebellion was finally crushed in mid-1916.

Total Allied casualties on the Ottoman fronts amounted 650,000 men. Total Ottoman casualties were 725,000 (325,000 dead and 400,000 wounded).

Italian participation
Italy had been allied with the German and Austro-Hungarian Empires since 1882 as part of the Triple Alliance. However, the nation had its own designs on Austrian territory in, the , (Rijeka) and. Rome had a secret 1902 pact with France, effectively nullifying its part in the Triple Alliance; Italy secretly agreed with France to remain neutral if the latter was attacked by Germany. At the start of hostilities, Italy refused to commit troops, arguing that the Triple Alliance was defensive and that Austria-Hungary was an aggressor. The Austro-Hungarian government began negotiations to secure Italian neutrality, offering the French colony of Tunisia in return. The Allies made a counter-offer in which Italy would receive the, Austrian Littoral and territory on the Dalmatian coast after the defeat of Austria-Hungary. This was formalised by the. Further encouraged by the Allied invasion of Turkey in April 1915, Italy joined the Triple Entente and declared war on Austria-Hungary on 23 May. Fifteen months later, Italy declared war on Germany.

The Italians had numerical superiority, but this advantage was lost, not only because of the difficult terrain in which the fighting took place, but also because of the strategies and tactics employed. , a staunch proponent of the frontal assault, had dreams of breaking into the Slovenian plateau, taking and threatening Vienna.

On the Trentino front, the Austro-Hungarians took advantage of the mountainous terrain, which favoured the defender. After an initial strategic retreat, the front remained largely unchanged, while Austrian and  engaged Italian  in bitter hand-to-hand combat throughout the summer. The Austro-Hungarians counterattacked in the, towards Verona and Padua, in the spring of 1916 (), but made little progress and were defeated by the Italians.

Beginning in 1915, the Italians under Cadorna mounted eleven offensives on the along the  (Soča) River, northeast of. Of these eleven offensives, five were won by Italy, three remained inconclusive, and the other three were repelled by the Austro-Hungarians, who held the higher ground. In the summer of 1916, after the, the Italians captured the town of. After this victory, the front remained static for over a year, despite several Italian offensives, centred on the and Karst Plateau east of Gorizia.

The Central Powers launched a crushing offensive on 26 October 1917, spearheaded by the Germans, and achieved a victory at. The Italian Army was routed and retreated more than 100 km to reorganise. The new Italian chief of staff,, ordered the Army to stop their retreat and defend the summit, where fortified defenses were constructed; the Italians repelled the Austro-Hungarian and German Army, and stabilised the front at the. Since the Italian Army had suffered heavy losses in the Battle of Caporetto, the Italian Government ordered conscription of the so-called '99 Boys (Ragazzi del '99): all males born in 1899 and prior, who were 18 years old or older. In 1918, the Austro-Hungarians failed to break through in a series of battles on the Piave and were finally decisively defeated in the in October. On 1November, the Italian Navy destroyed much of the Austro-Hungarian fleet stationed in, preventing it from being handed over to the new. On 3November, the Italians invaded Trieste from the sea. On the same day, the was signed. By mid-November 1918, the Italian military occupied the entire former Austrian Littoral and had seized control of the portion of Dalmatia that had been guaranteed to Italy by the London Pact. By the end of hostilities in November 1918, Admiral declared himself Italy's Governor of Dalmatia. Austria-Hungary surrendered on 11 November 1918.

Romanian participation
Romania had been allied with the Central Powers since 1882. When the war began, however, it declared its neutrality, arguing that because Austria-Hungary had itself declared war on Serbia, Romania was under no obligation to join the war. On 4August 1916, Romania and the Entente signed the Political Treaty and Military Convention, that established the coordinates of Romania's participation in the war. In return, it received the Allies' formal sanction for, and other territories of Austria-Hungary to be annexed to Romania. The action had large popular support. On 27 August 1916, the Romanian Army against Austria-Hungary, with limited Russian support. The Romanian offensive was initially successful in Transylvania, but a Central Powers counterattack by the drove them back. As a result of the, the Central Powers occupied Bucharest on 6December 1916. Fighting in Moldova, but Russian withdrawal from the war in late 1917 as a result of the meant that Romania was forced to sign an armistice with the Central Powers on 9December 1917.

In January 1918, Romanian forces established control over as the Russian Army abandoned the province. Although a treaty was signed by the Romanian and Russian governments following talks between 5and 9March 1918 on the withdrawal of Romanian forces from Bessarabia within two months, on 27 March 1918 Romania formally attached Bessarabia, inhabited by a Romanian majority, to its territory, based on a resolution passed by the local assembly of that territory on its unification with Romania.

Romania officially made peace with the Central Powers by signing the on 7May 1918. Under the treaty, Romania was obliged to end the war with the Central Powers and make small territorial concessions to Austria-Hungary, ceding control of some passes in the, and to grant oil concessions to Germany. In exchange, the Central Powers recognised the sovereignty of Romania over Bessarabia. The treaty was renounced in October 1918 by the government, and Romania nominally re-entered the war on 10 November 1918 against the Central Powers. The next day, the Treaty of Bucharest was nullified by the terms of the Armistice of. Total Romanian deaths from 1914 to 1918, military and civilian, within contemporary borders, were estimated at 748,000.

Initial actions
Russian plans for the start of the war called for simultaneous invasions of Austrian and East Prussia. Although Russia's initial advance into Galicia was largely successful, it was driven back from East Prussia by Hindenburg and at the battles of Tannenberg and the  in August and September 1914. Russia's less developed industrial base and ineffective military leadership were instrumental in the events that unfolded. By the spring of 1915, the Russians had retreated to Galicia, and, in May, the Central Powers achieved a remarkable breakthrough on Poland's southern frontiers with their. On 5August, they captured and forced the Russians to withdraw from Poland.

Russian Revolution
Despite Russia's success in the June 1916 against the Austrians in eastern Galicia, the offensive was undermined by the reluctance of other Russian generals to commit their forces to support the victory. Allied and Russian forces were revived only briefly by on 27 August, as Romania was rapidly defeated by a Central Powers offensive. Meanwhile, unrest grew in Russia as remained at the front. The increasingly incompetent rule of drew protests and resulted in the murder of her favourite,, at the end of 1916.

In March 1917, demonstrations in culminated in the abdication of Tsar Nicholas II and the appointment of a weak, which shared power with the  socialists. This arrangement led to confusion and chaos both at the front and at home. The army became increasingly ineffective.

Following the Tsar's abdication, —with the help of the German government—was ushered by train from Switzerland into Russia 16 April 1917. Discontent and the weaknesses of the Provisional Government led to a rise in the popularity of the Bolshevik Party, led by Lenin, which demanded an immediate end to the war. The Revolution of November was followed in December by an armistice and negotiations with Germany. At first, the Bolsheviks refused the German terms, but when German troops began marching across Ukraine unopposed, the new government acceded to the on 3March 1918. The treaty ceded vast territories, including Finland, the, parts of Poland and Ukraine to the Central Powers. Despite this enormous German success, the manpower required by the Germans to occupy the captured territory may have contributed to the failure of their, and secured relatively little food or other for the Central Powers war effort.

With the adoption of the Treaty of Brest-Litovsk, the Entente no longer existed. The Allied powers led of Russia, partly to stop Germany from exploiting Russian resources, and to a lesser extent, to support the  (as opposed to the "Reds") in the. Allied troops landed in and in  as part of the.

Czechoslovak Legion
The Czechoslovak Legion fought on the side of the Entente. Its goal was to win support for the independence of. The Legion in Russia was established in September 1914, in December 1917 in (including volunteers from America) and in April 1918 in. Czechoslovak Legion troops defeated the army at the Ukrainian village of, in July 1917. After this success, the number of Czechoslovak legionaries increased, as well as Czechoslovak military power. In the, the Legion defeated the Germans and forced them to make a truce.

In Russia, they were heavily involved in the Russian Civil War, siding with the Whites against the, at times controlling most of the and conquering all the major cities of. The presence of the Czechoslovak Legion near appears to have been one of the motivations for the Bolshevik  in July 1918. Legionaries arrived less than a week afterwards and captured the city. Because Russia's European ports were not safe, the corps was evacuated by a long detour via the port of Vladivostok. The last transport was the American ship Heffron in September 1920.

Central Powers peace overtures
On 12 December 1916, after ten brutal months of the Battle of Verdun and a, Germany attempted to negotiate a peace with the Allies. However, this attempt was rejected out of hand as a "duplicitous war ruse".

Soon after, the US President, Woodrow Wilson, attempted to intervene as a peacemaker, asking in a note for both sides to state their demands. War Cabinet considered the German offer to be a ploy to create divisions amongst the Allies. After initial outrage and much deliberation, they took Wilson's note as a separate effort, signalling that the United States was on the verge of entering the war against Germany following the "submarine outrages". While the Allies debated a response to Wilson's offer, the Germans chose to rebuff it in favour of "a direct exchange of views". Learning of the German response, the Allied governments were free to make clear demands in their response of 14 January. They sought restoration of damages, the evacuation of occupied territories, reparations for France, Russia and Romania, and a recognition of the principle of nationalities. This included the liberation of Italians, Slavs, Romanians, Czecho-Slovaks, and the creation of a "free and united Poland". On the question of security, the Allies sought guarantees that would prevent or limit future wars, complete with sanctions, as a condition of any peace settlement. The negotiations failed and the Entente powers rejected the German offer on the grounds that Germany had not put forward any specific proposals.

1917–1918
Events of 1917 proved decisive in ending the war, although their effects were not fully felt until 1918.

Developments in 1917
The British naval blockade began to have a serious impact on Germany. In response, in February 1917, the convinced  Theobald von Bethmann-Hollweg to declare unrestricted submarine warfare, with the goal of starving Britain out of the war. German planners estimated that unrestricted submarine warfare would cost Britain a monthly shipping loss of 600,000 tons. The General Staff acknowledged that the policy would almost certainly bring the United States into the conflict, but calculated that British shipping losses would be so high that they would be forced to sue for peace after five to six months, before American intervention could have an effect. Tonnage sunk rose above 500,000 tons per month from February to July. It peaked at 860,000 tons in April. After July, the newly re-introduced system became effective in reducing the U-boat threat. Britain was safe from starvation, while German industrial output fell, and the United States joined the war far earlier than Germany had anticipated.

On 3 May 1917, during the Nivelle Offensive, the French 2nd Colonial Division, veterans of the Battle of Verdun, refused orders, arriving drunk and without their weapons. Their officers lacked the means to punish an entire division, and harsh measures were not immediately implemented. The French Army Mutinies eventually spread to a further 54 French divisions, and 20,000 men deserted. However, appeals to patriotism and duty, as well as mass arrests and trials, encouraged the soldiers to return to defend their trenches, although the French soldiers refused to participate in further offensive action. was removed from command by 15 May, replaced by General, who suspended bloody large-scale attacks.

The victory of the Central Powers at the Battle of Caporetto led the Allies to convene the at which they formed the  to co-ordinate planning. Previously, British and French armies had operated under separate commands.

In December, the Central Powers signed an armistice with Russia, thus freeing large numbers of German troops for use in the west. With German reinforcements and new American troops pouring in, the outcome was to be decided on the Western Front. The Central Powers knew that they could not win a protracted war, but they held high hopes for success based on a final quick offensive. Furthermore, both sides became increasingly fearful of social unrest and revolution in Europe. Thus, both sides urgently sought a decisive victory.

In 1917, Emperor secretly attempted separate peace negotiations with Clemenceau, through his wife's brother  in Belgium as an intermediary, without the knowledge of Germany. Italy opposed the proposals. When the negotiations failed, his attempt was revealed to Germany, resulting in a diplomatic catastrophe.

Ottoman Empire conflict, 1917–1918
In March and April 1917, at the and, German and Ottoman forces stopped the advance of the Egyptian Expeditionary Force, which had begun in August 1916 at the Battle of Romani. At the end of October, the resumed, when General 's,  and  won the. Two Ottoman armies were defeated a few weeks later at the and, early in December,  was captured following another Ottoman defeat at the. About this time, was relieved of his duties as the Eighth Army's commander, replaced by, and a few months later the commander of the  in Palestine, , was replaced by.

In early 1918, the front line was and the  was occupied, following the  and the  attacks by British Empire forces in March and April 1918. In March, most of the Egyptian Expeditionary Force's British infantry and cavalry were sent to the Western Front as a consequence of the Spring Offensive. They were replaced by Indian Army units. During several months of reorganisation and training of the summer, a were carried out on sections of the Ottoman front line. These pushed the front line north to more advantageous positions for the Entente in preparation for an attack and to acclimatise the newly arrived Indian Army infantry. It was not until the middle of September that the integrated force was ready for large-scale operations.

The reorganised Egyptian Expeditionary Force, with an additional mounted division, broke Ottoman forces at the in September 1918. In two days the British and Indian infantry, supported by a creeping barrage, broke the Ottoman front line and captured the headquarters of the at, the continuous trench lines at , , and the  headquarters at. The Desert Mounted Corps rode through the break in the front line created by the infantry. During virtually continuous operations by, British mounted Yeomanry, Indian , and New Zealand brigades in the , they captured , , , along with  on the Mediterranean coast and  east of the Jordan River on the Hejaz railway. and on the  were captured on the way northwards to. Meanwhile, of Australian light horse, New Zealand mounted rifles, Indian, British West Indies and Jewish infantry captured the crossings of the, ,  and at Ziza most of the. The, signed at the end of October, ended hostilities with the Ottoman Empire when fighting was continuing north of.

15 August 1917: Peace offer by the Pope
On or shortly before 15 August 1917 made a peace proposal suggesting:
 * No annexations
 * No indemnities, except to compensate for severe war damage in Belgium and parts of France and of Serbia
 * A solution to the problems of, and
 * Restoration of the
 * Germany to pull out of Belgium and France
 * Germany's overseas colonies to be returned to Germany
 * General disarmament
 * A Supreme Court of arbitration to settle future disputes between nations
 * The freedom of the seas
 * Abolish all retaliatory economic conflicts
 * No point in ordering reparations, because so much damage had been caused to all belligerents

Entry of the United States
At the outbreak of the war, the United States pursued a policy of, avoiding conflict while trying to broker a peace. When the German U-boat  on 7May 1915 with 128 Americans among the dead, President  insisted that America is "too proud to fight" but demanded an end to attacks on passenger ships. Germany complied. Wilson unsuccessfully tried to mediate a settlement. However, he also repeatedly warned that the United States would not tolerate unrestricted submarine warfare, in violation of international law. Former president denounced German acts as "piracy". Wilson was narrowly re-elected in after campaigning with the slogan "he kept us out of war".

In January 1917, Germany decided to resume unrestricted submarine warfare, in the hopes of starving Britain into surrender. Germany did this realising it would mean American entry. The German Foreign Minister, in the, invited Mexico to join the war as Germany's ally against the United States. In return, the Germans would finance Mexico's war and help it recover the territories of Texas, New Mexico, and Arizona. The United Kingdom intercepted the message and presented it to the US embassy in the UK. From there it made its way to President Wilson who released the Zimmermann note to the public, and Americans saw it as . Wilson called on anti-war elements to end all wars, by winning this one and eliminating militarism from the globe. He argued that the war was so important that the US had to have a voice in the peace conference. After the sinking of seven US merchant ships by submarines and the publication of the Zimmermann telegram, Wilson called for war on Germany on 2April 1917, which the.

The United States was never formally a member of the Allies but became a self-styled "Associated Power". The United States had a small army, but, after the passage of the, it drafted 2.8 million men, and, by summer 1918, was sending 10,000 fresh soldiers to France every day. In 1917, the US Congress granted US citizenship to Puerto Ricans to allow them to be drafted to participate in World WarI, as part of the. German General Staff assumptions that it would be able to defeat the British and French forces before American troops reinforced them were proven incorrect.

The sent a  to  to join with the British Grand Fleet, destroyers to, , and s to help guard convoys. Several regiments of were also dispatched to France. The British and French wanted American units used to reinforce their troops already on the battle lines and not waste scarce shipping on bringing over supplies. General, (AEF) commander, refused to break up American units to be used as filler material. As an exception, he did allow African-American combat regiments to be used in French divisions. The fought as part of the French 16th Division, and earned a unit  for their actions at, , and Sechault. AEF doctrine called for the use of frontal assaults, which had long since been discarded by British Empire and French commanders due to the large loss of life that resulted.

German Spring Offensive of 1918
Ludendorff drew up plans for the 1918 offensive on the Western Front. The Spring Offensive sought to divide the British and French forces with a series of feints and advances. The German leadership hoped to end the war before significant US forces arrived. The operation commenced on 21 March 1918 with an attack on British forces near. German forces achieved an unprecedented advance of 60 km.

British and French trenches were penetrated using novel, also named Hutier tactics after General , by specially trained units called. Previously, attacks had been characterised by long artillery bombardments and massed assaults. In the Spring Offensive of 1918, however, Ludendorff used artillery only briefly and infiltrated small groups of infantry at weak points. They attacked command and logistics areas and bypassed points of serious resistance. More heavily armed infantry then destroyed these isolated positions. This German success relied greatly on the element of surprise.

The front moved to within 120 km of Paris. Three heavy s fired 183 shells on the capital, causing many Parisians to flee. The initial offensive was so successful that Kaiser Wilhelm II declared 24 March a. Many Germans thought victory was near. After heavy fighting, however, the offensive was halted. Lacking tanks or, the Germans were unable to consolidate their gains. The problems of re-supply were also exacerbated by increasing distances that now stretched over terrain that was shell-torn and often impassable to traffic.

pressed to use the arriving American troops as individual replacements, whereas Pershing sought to field American units as an independent force. These units were assigned to the depleted French and British Empire commands on 28 March. A Supreme War Council of Allied forces was created at the on 5November 1917. General Foch was appointed as supreme commander of the Allied forces. Haig, Petain, and Pershing retained tactical control of their respective armies; Foch assumed a co-ordinating rather than a directing role, and the British, French, and US commands operated largely independently.

Following Operation Michael, Germany launched against the northern  ports. The Allies halted the drive after limited territorial gains by Germany. The German Army to the south then conducted, pushing broadly towards Paris. Germany launched Operation Marne on 15 July, in an attempt to encircle. The resulting counter-attack, which started the, marked the first successful Allied offensive of the war. By 20 July, the Germans had retreated across the Marne to their starting lines, having achieved little, and the German Army never regained the initiative. German casualties between March and April 1918 were 270,000, including many highly trained stormtroopers.

Meanwhile, Germany was falling apart at home. marches became frequent and morale in the army fell. Industrial output was half the 1913 levels.

New states enter the war
In the late spring of 1918, three new states were formed in the : the, the , and the , which declared their independence from the Russian Empire. Two other minor entities were established, the and  (the former was liquidated by Azerbaijan in the autumn of 1918 and the latter by a joint Armenian-British task force in early 1919). With the withdrawal of the Russian armies from the Caucasus front in the winter of 1917–18, the three major republics braced for an imminent Ottoman advance, which commenced in the early months of 1918. Solidarity was briefly maintained when the was created in the spring of 1918, but this collapsed in May, when the Georgians  from Germany and the Azerbaijanis concluded a treaty with the Ottoman Empire that was more akin to a military alliance. Armenia was left to fend for itself and struggled for five months against the threat of a full-fledged occupation by the Ottoman Turks before defeating them at the.

Hundred Days Offensive
The Allied counteroffensive, known as the Hundred Days Offensive, began on 8August 1918, with the. The battle involved over 400 tanks and 120,000 British,, and French troops, and by the end of its first day a gap 24 km long had been created in the German lines. The defenders displayed a marked collapse in morale, causing Ludendorff to refer to this day as the "Black Day of the German army". After an advance as far as 23 km, German resistance stiffened, and the battle was concluded on 12 August.

Rather than continuing the Amiens battle past the point of initial success, as had been done so many times in the past, the Allies shifted attention elsewhere. Allied leaders had now realised that to continue an attack after resistance had hardened was a waste of lives, and it was better to turn a line than to try to roll over it. They began to undertake attacks in quick order to take advantage of successful advances on the flanks, then broke them off when each attack lost its initial impetus.

The day after the Offensive began, Ludendorff said: "We cannot win the war any more, but we must not lose it either." On 11 August he offered his resignation to the Kaiser, who refused it, replying, "I see that we must strike a balance. We have nearly reached the limit of our powers of resistance. The war must be ended." On 13 August, at, Hindenburg, Ludendorff, the Chancellor, and Foreign Minister Hintz agreed that the war could not be ended militarily and, on the following day, the German Crown Council decided that victory in the field was now most improbable. Austria and Hungary warned that they could continue the war only until December, and Ludendorff recommended immediate peace negotiations. Prince Rupprecht warned Prince Max of Baden: "Our military situation has deteriorated so rapidly that I no longer believe we can hold out over the winter; it is even possible that a catastrophe will come earlier."

Battle of Albert
British and Dominion forces launched the next phase of the campaign with the on 21 August. The assault was widened by French and then further British forces in the following days. During the last week of August the Allied pressure along a 110 km front against the enemy was heavy and unrelenting. From German accounts, "Each day was spent in bloody fighting against an ever and again on-storming enemy, and nights passed without sleep in retirements to new lines."

Faced with these advances, on 2 September the German issued orders to withdraw in the south to the. This ceded without a fight the seized the previous April. According to Ludendorff, "We had to admit the necessity ... to withdraw the entire front from the Scarpe to the Vesle. In nearly four weeks of fighting beginning on 8August, over 100,000 German prisoners were taken. The German High Command realised that the war was lost and made attempts to reach a satisfactory end. On 10 September Hindenburg urged peace moves to Emperor Charles of Austria, and Germany appealed to the Netherlands for mediation. On 14 September Austria sent a note to all belligerents and neutrals suggesting a meeting for peace talks on neutral soil, and on 15 September Germany made a peace offer to Belgium. Both peace offers were rejected.

Allied advance to the Hindenburg Line
In September the Allies in the north and centre. The Germans continued to fight strong rear-guard actions and launched numerous counterattacks, but positions and outposts of the Line continued to fall, with the BEF alone taking 30,441 prisoners in the last week of September. On 24 September an assault by both the British and French came within 3 km of St. Quentin. The Germans had now retreated to positions along or behind the Hindenburg Line. That same day, Supreme Army Command informed the leaders in Berlin that armistice talks were inevitable.

The on the Hindenburg Line began with the, launched by French and American troops on 26 September. The following week, co-operating French and American units broke through in at the, forcing the Germans off the commanding heights, and closing towards the Belgian frontier. On 8October the line was pierced again by British and Dominion troops at the. The German army had to shorten its front and use the Dutch frontier as an anchor to fight rear-guard actions as it fell back towards Germany.

When Bulgaria signed a separate armistice on 29 September, Ludendorff, having been under great stress for months, suffered something similar to a breakdown. It was evident that Germany could no longer mount a successful defence. The collapse of the Balkans meant that Germany was about to lose its main supplies of oil and food. Its reserves had been used up, even as US troops kept arriving at the rate of 10,000 per day. The Americans supplied more than 80% of Allied oil during the war, and there was no shortage.

German Revolution 1918–1919
News of Germany's impending military defeat spread throughout the German armed forces. The threat of mutiny was rife. Admiral Reinhard Scheer and Ludendorff decided to launch a last attempt to restore the "valour" of the German Navy.

In northern Germany, the began at the end of October 1918. Units of the German Navy refused to set sail for a last, large-scale operation in a war they believed to be as good as lost, initiating the uprising. The, which then ensued in the naval ports of and , spread across the whole country within days and led to the proclamation of a republic on 9November 1918, shortly thereafter to the abdication of Kaiser Wilhelm II, and to German surrender.

New German government surrenders
With the military faltering and with widespread loss of confidence in the Kaiser leading to his abdication and fleeing of the country, Germany moved towards surrender. Prince Maximilian of Baden took charge of a new government on 3October as Chancellor of Germany to negotiate with the Allies. Negotiations with President Wilson began immediately, in the hope that he would offer better terms than the British and French. Wilson demanded a constitutional monarchy and parliamentary control over the German military. There was no resistance when the  on 9November declared Germany to be a republic. The Kaiser, kings and other hereditary rulers all were removed from power and Wilhelm fled to exile in. Imperial Germany was dead; a new Germany had been born as the.

Armistices and capitulations
The collapse of the Central Powers came swiftly. Bulgaria was the first to sign an armistice, the on 29 September 1918. German Emperor in his telegram to  described situation: “Disgraceful! 62,000 Serbs decided the war!". On 29 September 1918, the informed  and the  , that the military situation facing Germany was hopeless.

On 30 October, the Ottoman Empire capitulated, signing the Armistice of Mudros.

On 24 October, the Italians began a push that rapidly recovered territory lost after the Battle of Caporetto. This culminated in the Battle of Vittorio Veneto, which marked the end of the Austro-Hungarian Army as an effective fighting force. The offensive also triggered the disintegration of the Austro-Hungarian Empire. During the last week of October, declarations of independence were made in Budapest, Prague, and Zagreb. On 29 October, the imperial authorities asked Italy for an armistice, but the Italians continued advancing, reaching Trento, Udine, and Trieste. On 3November, Austria-Hungary sent a to ask for an  (Armistice of Villa Giusti). The terms, arranged by telegraph with the Allied Authorities in Paris, were communicated to the Austrian commander and accepted. The Armistice with Austria was signed in the Villa Giusti, near, on 3November. Austria and Hungary signed separate armistices following the overthrow of the. In the following days the Italian Army occupied and all  with over 20,000 soldiers.

On 11 November, at 5:00 am, an was signed in a railroad carriage at Compiègne. At 11 am on 11 November 1918—"the eleventh hour of the eleventh day of the eleventh month"—a ceasefire came into effect. During the six hours between the signing of the armistice and its taking effect, opposing armies on the Western Front began to withdraw from their positions, but fighting continued along many areas of the front, as commanders wanted to capture territory before the war ended. The took place following the Armistice. The occupying armies consisted of American, Belgian, British and French forces.

In November 1918, the Allies had ample supplies of men and materiel to invade Germany. Yet at the time of the armistice, no Allied force had crossed the German frontier, the Western Front was still some 720 km from Berlin, and the Kaiser's armies had retreated from the battlefield in good order. These factors enabled Hindenburg and other senior German leaders to spread the story that their armies had not really been defeated. This resulted in the, which attributed Germany's defeat not to its inability to continue fighting (even though up to a million soldiers were suffering from the and unfit to fight), but to the public's failure to respond to its "patriotic calling" and the supposed intentional sabotage of the war effort, particularly by Jews, Socialists, and Bolsheviks.

The Allies had much more potential wealth they could spend on the war. One estimate (using 1913 US dollars) is that the Allies spent $58 billion on the war and the Central Powers only $25 billion. Among the Allies, the UK spent $21 billion and the US$17 billion; among the Central Powers Germany spent $20 billion.

Aftermath
In the aftermath of the war, four empires disappeared: the German, Austro-Hungarian, Ottoman, and Russian. Numerous nations regained their former independence, and new ones were created. Four dynasties, together with their ancillary aristocracies, fell as a result of the war: the, the , the s, and the. Belgium and Serbia were badly damaged, as was France, with 1.4 million soldiers dead, not counting other casualties. Germany and Russia were similarly affected.

Formal end of the war
A formal state of war between the two sides persisted for another seven months, until the signing of the with Germany on 28 June 1919. The United States Senate did not ratify the treaty despite public support for it, and did not formally end its involvement in the war until the was signed on 2July 1921 by President. For the United Kingdom and the British Empire, the state of war ceased under the provisions of the  with respect to:


 * Germany on 10 January 1920.
 * Austria on 16 July 1920.
 * Bulgaria on 9 August 1920.
 * Hungary on 26 July 1921.
 * Turkey on 6 August 1924.

After the Treaty of Versailles, treaties with Austria, Hungary, Bulgaria, and the Ottoman Empire were signed. However, the negotiation of the treaty with the Ottoman Empire was followed by strife, and a final peace treaty between the Allied Powers and the country that would shortly become the was not signed until 24 July 1923, at.

Some s date the end of the war as being when the Versailles Treaty was signed in 1919, which was when many of the troops serving abroad finally returned home; by contrast, most commemorations of the war's end concentrate on the armistice of 11 November 1918. Legally, the formal peace treaties were not complete until the last, the Treaty of Lausanne, was signed. Under its terms, the Allied forces left on 23 August 1923.

Peace treaties and national boundaries
After the war, the imposed a series of peace treaties on the Central Powers officially ending the war. The 1919 dealt with Germany and, building on, brought into being the  on 28 June 1919.

The Central Powers had to acknowledge responsibility for "all the loss and damage to which the Allied and Associated Governments and their nationals have been subjected as a consequence of the war imposed upon them by" their aggression. In the Treaty of Versailles, this statement was. This article became known as the War Guilt clause as the majority of Germans felt humiliated and resentful. Overall the Germans felt they had been unjustly dealt with by what they called the " of Versailles". German historian Hagen Schulze said the Treaty placed Germany "under legal sanctions, deprived of military power, economically ruined, and politically humiliated." Belgian historian Laurence Van Ypersele emphasises the central role played by memory of the war and the Versailles Treaty in German politics in the 1920s and 1930s: "Active denial of war guilt in Germany and German resentment at both reparations and continued Allied occupation of the Rhineland made widespread revision of the meaning and memory of the war problematic. The legend of the '' and the wish to revise the 'Versailles diktat', and the belief in an international threat aimed at the elimination of the German nation persisted at the heart of German politics. Even a man of peace such as [ ] Stresemann publicly rejected German guilt. As for the Nazis, they waved the banners of domestic treason and international conspiracy in an attempt to galvanise the German nation into a spirit of revenge. Like a Fascist Italy, Nazi Germany sought to redirect the memory of the war to the benefit of its own policies."

Meanwhile, new nations liberated from German rule viewed the treaty as recognition of wrongs committed against small nations by much larger aggressive neighbours. The Peace Conference required all the defeated powers to pay for all the damage done to civilians. However, owing to economic difficulties and Germany being the only defeated power with an intact economy, the burden fell largely on Germany.

Austria-Hungary was partitioned into several successor states, including Austria, Hungary, Czechoslovakia, and, largely but not entirely along ethnic lines. Transylvania was shifted from Hungary to. The details were contained in the and the Treaty of Trianon. As a result of the, 3.3 million Hungarians came under foreign rule. Although the Hungarians made up approximately 54% of the population of the pre-war (according to the ), only 32% of its territory was left to Hungary. Between 1920 and 1924, 354,000 Hungarians fled former Hungarian territories attached to Romania, Czechoslovakia, and Yugoslavia.

The Russian Empire, which had withdrawn from the war in 1917 after the October Revolution, lost much of its western frontier as the newly independent nations of, , , , and were carved from it. Romania took control of Bessarabia in April 1918.

The Ottoman Empire disintegrated, with much of its territory awarded to various Allied powers as protectorates. The Turkish core in was reorganised as the Republic of Turkey. The Ottoman Empire was to be partitioned by the of 1920. This treaty was never ratified by the Sultan and was rejected by the, leading to the victorious and the much less stringent 1923 Treaty of Lausanne.

Even though a lot of countries had already made a peace treaty, there was one exception,. Andorra declared war on Germany in August 1914, but, because it had a very small population, Andorra had never sent any soldiers to the battlefield. Because of that, Andorra was not allowed to go to the Treaty of Versailles, so the country had not made a peace treaty with Germany until 1958. When Andorra made the declaration of war, it had an army of 600 part-time militarymen, commanded by two officials.

National identities
After 123 years, Poland re-emerged as an independent country. The Kingdom of Serbia and its dynasty, as a "minor Entente nation" and the country with the most casualties per capita, became the backbone of a new multinational state, the, later renamed Yugoslavia. Czechoslovakia, combining the with parts of the Kingdom of Hungary, became a new nation. Russia became the and lost Finland, Estonia, Lithuania, and Latvia, which became independent countries. The was soon replaced by Turkey and several other countries in the Middle East.

In the British Empire, the war unleashed new forms of nationalism. In Australia and New Zealand the Battle of Gallipoli became known as those nations' "Baptism of Fire". It was the first major war in which the newly established countries fought, and it was one of the first times that Australian troops fought as Australians, not just subjects of the. , commemorating the Australian and New Zealand Army Corps (ANZAC), celebrates this defining moment.

After the Battle of Vimy Ridge, where the Canadian divisions fought together for the first time as a single corps, Canadians began to refer to their country as a nation "forged from fire". Having succeeded on the same battleground where the "mother countries" had previously faltered, they were for the first time respected internationally for their own accomplishments. Canada entered the war as a Dominion of the British Empire and remained so, although it emerged with a greater measure of independence. When Britain declared war in 1914, the dominions were automatically at war; at the conclusion, Canada, Australia, New Zealand, and South Africa were individual signatories of the Treaty of Versailles.

Lobbying by and fear that American Jews would encourage the United States to support Germany culminated in the British government's  of 1917, endorsing creation of a  in Palestine. A total of more than 1,172,000 Jewish soldiers served in the Allied and Central Power forces in World WarI, including 275,000 in Austria-Hungary and 450,000 in Tsarist Russia.

The establishment of the modern state of Israel and the roots of the continuing are partially found in the unstable power dynamics of the Middle East that resulted from World WarI. Before the end of the war, the Ottoman Empire had maintained a modest level of peace and stability throughout the Middle East. With the fall of the Ottoman government, power vacuums developed and conflicting claims to land and nationhood began to emerge. The political boundaries drawn by the victors of World WarI were quickly imposed, sometimes after only cursory consultation with the local population. These continue to be problematic in the 21st-century struggles for. While the dissolution of the Ottoman Empire at the end of World WarI was pivotal in contributing to the modern political situation of the Middle East, including the, the end of Ottoman rule also spawned lesser known disputes over water and other natural resources.

The prestige of Germany and German things in remained high after the war but did not recovered to its pre-war levels. Indeed, in the war bought an end to a period of intense scientific and cultural influence writer  scorningly called "the German bewichment" (el embrujamiento alemán).

Health effects
Of the 60 million European military personnel who were mobilised from 1914 to 1918,, 7 million were permanently disabled, and 15 million were seriously injured. Germany lost 15.1% of its active male population, Austria-Hungary lost 17.1%, and France lost 10.5%. In Germany, civilian deaths were 474,000 higher than in peacetime, due in large part to food shortages and malnutrition that weakened resistance to disease. By the end of the war, starvation caused by famine had killed approximately 100,000 people in Lebanon. Between 5and 10 million people died in the. By 1922, there were between 4.5 million and 7million homeless children in Russia as a result of nearly a decade of devastation from World WarI, the Russian Civil War, and the subsequent famine of 1920–1922. Numerous anti-Soviet Russians fled the country after the Revolution; by the 1930s, the northern Chinese city of had 100,000 Russians. Thousands more emigrated to France, England, and the United States.

The Australian prime minister,, wrote to the British prime minister, , "You have assured us that you cannot get better terms. I much regret it, and hope even now that some way may be found of securing agreement for demanding reparation commensurate with the tremendous sacrifices made by the British Empire and her Allies." Australia received £5,571,720 war reparations, but the direct cost of the war to Australia had been £376,993,052, and, by the mid-1930s, repatriation pensions, war gratuities, interest and sinking fund charges were £831,280,947. Of about 416,000 Australians who served, about 60,000 were killed and another 152,000 were wounded.

Diseases flourished in the chaotic wartime conditions. In 1914 alone, louse-borne killed 200,000 in Serbia. From 1918 to 1922, Russia had about 25 million infections and 3million deaths from epidemic typhus. In 1923, 13 million Russians contracted malaria, a sharp increase from the pre-war years. In addition, a major influenza epidemic spread around the world. Overall, the 1918 flu pandemic killed at least 50 million people. Moreover, between 1915 and 1926, an epidemic of spread around the world affecting nearly five million people.

The social disruption and widespread violence of the Russian Revolution of 1917 and the ensuing sparked more than 2,000 s in the former Russian Empire, mostly in. An estimated 60,000–200,000 civilian Jews were killed in the atrocities.

In the aftermath of World War I, Greece against Turkish nationalists led by, a war that eventually resulted in a  under the Treaty of Lausanne. According to various sources, several hundred thousand Greeks died during this period, which was tied in with the Greek Genocide.

Ground warfare
World War I began as a clash of 20th-century technology and 19th-century, with the inevitably large ensuing casualties. By the end of 1917, however, the major armies, now numbering millions of men, had modernised and were making use of telephone,, , s, and aircraft. Infantry formations were reorganised, so that 100-man companies were no longer the main unit of manoeuvre; instead, squads of 10 or so men, under the command of a junior NCO, were favoured.

Artillery also underwent a revolution. In 1914, cannons were positioned in the front line and fired directly at their targets. By 1917, with guns (as well as mortars and even machine guns) was commonplace, using new techniques for spotting and ranging, notably aircraft and the often overlooked. missions became commonplace, also, and sound detection was used to locate enemy batteries.

Germany was far ahead of the Allies in using heavy indirect fire. The German Army employed 150 mm and 210 mm s in 1914, when typical French and British guns were only 75 mm and 105 mm. The British had a 6-inch (152 mm) howitzer, but it was so heavy it had to be hauled to the field in pieces and assembled. The Germans also fielded Austrian 305 mm and 420 mm guns and, even at the beginning of the war, had inventories of various calibres of , which were ideally suited for trench warfare.

On 27 June 1917 the Germans used the biggest gun in the world,, nicknamed "". This gun from Krupp was able to shoot 750 kg shells from to, a distance of about 50 km.

Much of the combat involved trench warfare, in which hundreds often died for each metre gained. Many of the deadliest battles in history occurred during World WarI. Such battles include Ypres, the Marne,, the Somme, Verdun, and Gallipoli. The Germans employed the of  to provide their forces with a constant supply of gunpowder despite the British naval blockade. Artillery was responsible for the largest number of casualties and consumed vast quantities of explosives. The large number of head wounds caused by exploding shells and forced the combatant nations to develop the modern steel helmet, led by the French, who introduced the  in 1915. It was quickly followed by the, worn by British Imperial and US troops, and in 1916 by the distinctive German , a design, with improvements, still in use today.

"Gas! GAS! Quick, boys! – An ecstasy of fumbling, Fitting the clumsy helmets just in time; But someone still was yelling out and stumbling, And flound'ring like a man in fire or lime ... Dim, through the misty panes and thick green light, As under a green sea, I saw him drowning."

-, , 1917

The widespread use of chemical warfare was a distinguishing feature of the conflict. Gases used included chlorine, and. Relatively few war casualties were caused by gas, as effective countermeasures to gas attacks were quickly created, such as s. The use of and small-scale  (as opposed to ) were both outlawed by the Hague Conventions of 1899 and 1907, and both proved to be of limited effectiveness, though they captured the public imagination.

The most powerful land-based weapons were railway guns, weighing dozens of tons apiece. The German version were nicknamed, even though the namesake was not a railway gun. Germany developed the, able to bombard Paris from over 100 km, though shells were relatively light at 94 kilograms (210 lb).

Trenches, machine guns, air reconnaissance, barbed wire, and modern artillery with fragmentation helped bring the battle lines of World WarI to a stalemate. The British and the French sought a solution with the creation of the tank and. The British were used during the Battle of the Somme on 15 September 1916. Mechanical reliability was an issue, but the experiment proved its worth. Within a year, the British were fielding tanks by the hundreds, and they showed their potential during the Battle of Cambrai in November 1917, by breaking the Hindenburg Line, while teams captured 8,000 enemy soldiers and 100 guns. Meanwhile, the French introduced the first tanks with a rotating turret, the, which became a decisive tool of the victory. The conflict also saw the introduction of and s, such as the, the , and the.

Another new weapon, the, was first used by the German army and later adopted by other forces. Although not of high tactical value, the flamethrower was a powerful, demoralising weapon that caused terror on the battlefield.

evolved to supply the enormous quantities of food, water, and ammunition required to support large numbers of soldiers in areas where conventional transportation systems had been destroyed. Internal combustion engines and improved traction systems for automobiles and trucks/lorries eventually rendered trench railways obsolete.

Areas taken in major attacks
On the Western Front neither side made impressive gains in the first three years of the war with attacks at Verdun, the Somme, Passchendaele, and Cambrai — the exception was Nivelle's Offensive in which the German defence gave ground while mauling the attackers so badly that there were mutinies in the French Army. In 1918 the Germans smashed through the defence lines in three great attacks: Michael, on the Lys, and on the Aisne, which displayed the power of their new tactics. The Allies struck back at, which showed the Germans that they must return to the defensive, and at Amiens; tanks played a prominent role in both these assaults, as they had the year before at Cambrai.

The areas in the East were larger. The Germans did well at the First Masurian Lakes driving the invaders from East Prussia, and at, which led the Russians to sue for peace. The Austro-Hungarians and Germans joined for a great success at Gorlice–Tarnów, which drove the Russians out of Poland. In a series of attacks along with the Bulgarians they occupied Serbia, Albania, Montenegro and most of Romania. The Allies successes came later in, the beginning of the end for the Ottomans, in Macedonia, which drove the Bulgarians out of the war, and at Vittorio Veneto, the final blow for the Austro-Hungarians. The area occupied in East by the Central powers on 11 November 1918 was 1042600 km2.

Naval
Germany deployed U-boats (submarines) after the war began. Alternating between restricted and unrestricted submarine warfare in the Atlantic, the employed them to deprive the British Isles of vital supplies. The deaths of British merchant sailors and the seeming invulnerability of U-boats led to the development of depth charges (1916), hydrophones (passive, 1917), blimps, s (, 1917), forward-throwing s, and dipping hydrophones (the latter two both abandoned in 1918). To extend their operations, the Germans proposed supply submarines (1916). Most of these would be forgotten in the until World WarII revived the need.

Aviation
were first used militarily by the Italians in Libya on 23 October 1911 during the for reconnaissance, soon followed by the dropping of grenades and  the next year. By 1914, their military utility was obvious. They were initially used for and. To shoot down enemy planes, and  were developed. s were created, principally by the Germans and British, though the former used s as well. Towards the end of the conflict, aircraft carriers were used for the first time, with HMS Furious launching in a raid to destroy the Zeppelin hangars at  in 1918.

Manned s, floating high above the trenches, were used as stationary reconnaissance platforms, reporting enemy movements and directing artillery. Balloons commonly had a crew of two, equipped with s, so that if there was an enemy air attack the crew could parachute to safety. At the time, parachutes were too heavy to be used by pilots of aircraft (with their marginal power output), and smaller versions were not developed until the end of the war; they were also opposed by the British leadership, who feared they might promote cowardice.

Recognised for their value as observation platforms, balloons were important targets for enemy aircraft. To defend them against air attack, they were heavily protected by antiaircraft guns and patrolled by friendly aircraft; to attack them, unusual weapons such as air-to-air rockets were tried. Thus, the reconnaissance value of blimps and balloons contributed to the development of air-to-air combat between all types of aircraft, and to the trench stalemate, because it was impossible to move large numbers of troops undetected. The Germans conducted air raids on England during 1915 and 1916 with airships, hoping to damage British morale and cause aircraft to be diverted from the front lines, and indeed the resulting panic led to the diversion of several squadrons of fighters from France.

Baralong incidents
On 19 August 1915, the German submarine was sunk by the British  HMS Baralong. All German survivors were by Baralong's crew on the orders of Lieutenant, the captain of the ship. The shooting was reported to the media by American citizens who were on board the Nicosia, a British freighter loaded with war supplies, which was stopped by U-27 just minutes before the incident.

On 24 September, Baralong destroyed, which was in the process of sinking the cargo ship Urbino. According to Karl Goetz, the submarine's commander, Baralong continued to fly the US flag after firing on U-41 and then rammed the lifeboat—carrying the German survivors—sinking it.

Torpedoing of HMHS Llandovery Castle
The Canadian hospital ship was torpedoed by the German submarine  on 27 June 1918 in violation of international law. Only 24 of the 258 medical personnel, patients, and crew survived. Survivors reported that the U-boat surfaced and ran down the lifeboats, machine-gunning survivors in the water. The U-boat captain,, was charged with war crimes in Germany following the war, but escaped prosecution by going to the , beyond the jurisdiction of German courts.

Blockade of Germany
After the war, the German government claimed that approximately 763,000 German civilians died from and disease during the war because of the Allied blockade. An academic study done in 1928 put the death toll at 424,000. Germany protested that the Allies had used starvation as a weapon of war. Sally Marks argued that the German accounts of a hunger blockade are a "myth," as Germany did not face the starvation level of Belgium and the regions of Poland and northern France that it occupied. According to the British judge and legal philosopher, "The War Orders given by the Admiralty on 26 August [1914] were clear enough. All food consigned to Germany through neutral ports was to be captured and all food consigned to Rotterdam was to be presumed consigned to Germany. ... The British were determined on the starvation policy, whether or not it was lawful."

Chemical weapons in warfare
The German army was the first to successfully deploy chemical weapons during the Second Battle of Ypres (22 April – 25 May 1915), after German scientists working under the direction of at the  developed a method to weaponize. The use of chemical weapons was sanctioned by the German High Command in an effort to force Allied soldiers out of their entrenched positions, complementing rather than supplanting more lethal conventional weapons. In time, chemical weapons were deployed by all major belligerents throughout the war, inflicting approximately 1.3 million casualties, but relatively few fatalities: About 90,000 in total. For example, there were an estimated 186,000 British chemical weapons casualties during the war (80% of which were the result of exposure to the, introduced to the battlefield by the Germans in July 1917, which burns the skin at any point of contact and inflicts more severe lung damage than chlorine or ), and up to one-third of American casualties were caused by them. The Russian Army reportedly suffered roughly 500,000 chemical weapon casualties in World WarI. The use of chemical weapons in warfare was in direct violation of the and the, which prohibited their use.

The effect of poison gas was not limited to combatants. Civilians were at risk from the gases as winds blew the poison gases through their towns, and they rarely received warnings or alerts of potential danger. In addition to absent warning systems, civilians often did not have access to effective gas masks. An estimated 100,000–260,000 civilian casualties were caused by chemical weapons during the conflict and tens of thousands more (along with military personnel) died from scarring of the lungs, skin damage, and cerebral damage in the years after the conflict ended. Many commanders on both sides knew such weapons would cause major harm to civilians but nonetheless continued to use them. British  wrote in his diary, "My officers and I were aware that such weapons would cause harm to women and children living in nearby towns, as strong winds were common in the battlefront. However, because the weapon was to be directed against the enemy, none of us were overly concerned at all."

The war damaged chemistry's prestige in European societies, in particular the German variety.

Ottoman Empire
The of the Ottoman Empire's Armenian population, including mass deportations and executions, during the final years of the Ottoman Empire is considered. The Ottomans carried out organised and systematic massacres of the Armenian population at the beginning of the war and portrayed deliberately provoked acts of Armenian resistance as rebellions to justify further extermination. In early 1915, a number of Armenians volunteered to join the Russian forces and the Ottoman government used this as a pretext to issue the (Law on Deportation), which authorised the deportation of Armenians from the Empire's eastern provinces to Syria between 1915 and 1918. The Armenians were intentionally and a number were attacked by Ottoman brigands. While an exact number of deaths is unknown, the estimates 1.5 million. The government of Turkey has consistently, arguing that those who died were victims of inter-ethnic fighting, famine, or disease during World WarI; these claims are rejected by most historians.

Other ethnic groups were similarly attacked by the Ottoman Empire during this period, including Assyrians and, and some scholars consider those events to be part of the same policy of extermination. At least 250,000 Assyrian Christians, about half of the population, and 350,000–750,000 and  were killed between 1915 and 1922.

Russian Empire
Many pogroms accompanied the of 1917 and the ensuing Russian Civil War. 60,000–200,000 civilian Jews were killed in the atrocities throughout the former Russian Empire (mostly within the in present-day ). There were an estimated 7–12 million casualties during the, mostly civilians.

Rape of Belgium
The German invaders treated any resistance—such as sabotaging rail lines—as illegal and immoral, and shot the offenders and burned buildings in retaliation. In addition, they tended to suspect that most civilians were potential  and, accordingly, took and sometimes killed hostages from among the civilian population. The German army executed over 6,500 French and Belgian civilians between August and November 1914, usually in near-random large-scale shootings of civilians ordered by junior German officers. The German Army destroyed 15,000–20,000 buildings—most famously the university library at —and generated a wave of refugees of over a million people. Over half the German regiments in Belgium were involved in major incidents. Thousands of workers were shipped to Germany to work in factories. British propaganda dramatising the attracted much attention in the United States, while Berlin said it was both lawful and necessary because of the threat of franc-tireurs like those in France in 1870. The British and French magnified the reports and disseminated them at home and in the United States, where they played a major role in dissolving support for Germany.

Soldiers' experiences
The British soldiers of the war were initially volunteers but increasingly were into service. Surviving veterans, returning home, often found they could discuss their experiences only amongst themselves. Grouping together, they formed "veterans' associations" or "Legions". A small number of personal accounts of American veterans have been collected by the.

Prisoners of war
About eight million men surrendered and were held in during the war. All nations pledged to follow the on fair treatment of, and the survival rate for POWs was generally much higher than that of combatants at the front. Individual surrenders were uncommon; large units usually surrendered en masse. At the siege of Maubeuge about 40,000 French soldiers surrendered, at the Russians took about 100,000 to 120,000 Austrian captives, at the Brusilov Offensive about 325,000 to 417,000 Germans and Austrians surrendered to Russians, and at the Battle of Tannenberg 92,000 Russians surrendered. When the besieged garrison of surrendered in 1915, some 20,000 Russians became prisoners, at the battle near  (February–March 1915) 14,000 Germans surrendered to Russians, and at the First Battle of the Marne about 12,000 Germans surrendered to the Allies. 25–31% of Russian losses (as a proportion of those captured, wounded, or killed) were to prisoner status; for Austria-Hungary 32%, for Italy 26%, for France 12%, for Germany 9%; for Britain 7%. Prisoners from the Allied armies totalled about 1.4 million (not including Russia, which lost 2.5–3.5 million men as prisoners). From the Central Powers about 3.3 million men became prisoners; most of them surrendered to Russians. Germany held 2.5 million prisoners; Russia held 2.2–2.9 million; while Britain and France held about 720,000. Most were captured just before the Armistice. The United States held 48,000. The most dangerous moment was the act of surrender, when helpless soldiers were sometimes gunned down. Once prisoners reached a camp, conditions were, in general, satisfactory (and much better than in World WarII), thanks in part to the efforts of the and inspections by neutral nations. However, conditions were terrible in Russia: starvation was common for prisoners and civilians alike; about 15–20% of the prisoners in Russia died, and in Central Powers imprisonment 8% of Russians. In Germany, food was scarce, but only 5% died.

The Ottoman Empire often treated POWs poorly. Some 11,800 British Empire soldiers, most of them Indians, became prisoners after the Siege of Kut in Mesopotamia in April 1916; 4,250 died in captivity. Although many were in a poor condition when captured, Ottoman officers forced them to march 1100 km to Anatolia. A survivor said: "We were driven along like beasts; to drop out was to die." The survivors were then forced to build a railway through the.

In Russia, when the prisoners from the of the Austro-Hungarian army were released in 1917, they re-armed themselves and briefly became a military and diplomatic force during the Russian Civil War.

While the Allied prisoners of the Central Powers were quickly sent home at the end of active hostilities, the same treatment was not granted to Central Power prisoners of the Allies and Russia, many of whom served as, e.g., in France until 1920. They were released only after many approaches by the Red Cross to the. German prisoners were still being held in Russia as late as 1924.

Military attachés and war correspondents
Military and civilian observers from every major power closely followed the course of the war. Many were able to report on events from a perspective somewhat akin to modern "" positions within the opposing land and naval forces.

Support for the war
In the Balkans, such as the leader,, strongly supported the war, desiring the freedom of  from Austria-Hungary and other foreign powers and the creation of an independent Yugoslavia. The, led by Trumbić, was formed in Paris on 30 April 1915 but shortly moved its office to London. In April 1918, the Rome Congress of Oppressed Nationalities met, including, , , , and Yugoslav representatives who urged the Allies to support national for the peoples residing within Austria-Hungary.

In the Middle East, soared in Ottoman territories in response to the rise of Turkish nationalism during the war, with Arab nationalist leaders advocating the creation of a  state. In 1916, the Arab Revolt began in Ottoman-controlled territories of the Middle East in an effort to achieve independence.

In East Africa, of  was supporting the  who were at war with the British in the. Von Syburg, the German envoy in, said, "now the time has come for Ethiopia to regain the coast of the Red Sea driving the Italians home, to restore the Empire to its ancient size." The Ethiopian Empire was on the verge of entering World WarI on the side of the Central Powers before Iyasu's overthrow due to Allied pressure on the Ethiopian aristocracy. Iyasu was accused of converting to. According to Ethiopian historian, the evidence used to prove Iyasu's conversion was a doctored photo of Iyasu wearing a turban provided by the Allies. Some historians claim the British spy forged the Iyasu photo.

A number of socialist parties initially supported the war when it began in August 1914. But European socialists split on national lines, with the concept of held by radical socialists such as Marxists and  being overborne by their patriotic support for the war. Once the war began, Austrian, British, French, German, and Russian socialists followed the rising nationalist current by supporting their countries' intervention in the war.

was stirred by the outbreak of the war and was initially strongly supported by a variety of political factions. One of the most prominent and popular Italian nationalist supporters of the war was, who promoted and helped sway the Italian public to support intervention in the war. The, under the leadership of , promoted intervention in the war on the side of the Allies and used the Dante Alighieri Society to promote Italian nationalism. Italian socialists were divided on whether to support the war or oppose it; some were militant supporters of the war, including and. However, the decided to oppose the war after anti-militarist protestors were killed, resulting in a  called. The Italian Socialist Party purged itself of pro-war nationalist members, including Mussolini. Mussolini, a syndicalist who supported the war on grounds of irredentist claims on Italian-populated regions of Austria-Hungary, formed the pro-interventionist ' and the Fasci Rivoluzionario d'Azione Internazionalista ("Revolutionary for International Action") in October 1914 that later developed into the ' in 1919, the origin of fascism. Mussolini's nationalism enabled him to raise funds from (an armaments firm) and other companies to create Il Popolo d'Italia to convince socialists and revolutionaries to support the war.

Opposition to the war
Once war was declared, many socialists and trade unions backed their governments. Among the exceptions were the Bolsheviks, the, the Italian Socialist Party, and people like , , and their followers in Germany.

, elected to the papacy less than three months into World WarI, made the war and its consequences the main focus of his early pontificate. In stark contrast to his, five days after his election he spoke of his determination to do what he could to bring peace. His first encyclical, , given 1November 1914, was concerned with this subject. Benedict XV found his abilities and unique position as a religious emissary of peace ignored by the belligerent powers. The 1915 Treaty of London between Italy and the Triple Entente included secret provisions whereby the Allies agreed with Italy to ignore papal peace moves towards the Central Powers. Consequently, the publication of Benedict's proposed of August 1917 was roundly ignored by all parties except Austria-Hungary.

In in 1914, the   annual camp was held at Tidworth Pennings, near. Head of the British Army,, was to review the s, but the imminence of the war prevented him. General was sent instead. He surprised the two-or-three thousand cadets by declaring (in the words of Donald Christopher Smith, a cadet who was present), "that war should be avoided at almost any cost, that war would solve nothing, that the whole of Europe and more besides would be reduced to ruin, and that the loss of life would be so large that whole populations would be decimated. In our ignorance I, and many of us, felt almost ashamed of a British General who uttered such depressing and unpatriotic sentiments, but during the next four years, those of us who survived the holocaust—probably not more than one-quarter of us—learned how right the General's prognosis was and how courageous he had been to utter it." Voicing these sentiments did not hinder Smith-Dorrien's career, or prevent him from doing his duty in World WarI to the best of his abilities.

Many countries jailed those who spoke out against the conflict. These included in the United States and  in Britain. In the US, the and  made it a federal crime to oppose military recruitment or make any statements deemed "disloyal". Publications at all critical of the government were removed from circulation by postal censors, and many served long prison sentences for statements of fact deemed unpatriotic.

A number of nationalists opposed intervention, particularly within states that the nationalists were hostile to. Although the vast majority of Irish people consented to participate in the war in 1914 and 1915, a minority of advanced staunchly opposed taking part. The war began amid the Home Rule crisis in Ireland that had resurfaced in 1912, and by July 1914 there was a serious possibility of an outbreak of civil war in Ireland. Irish nationalists and Marxists attempted to pursue Irish independence, culminating in the of 1916, with Germany sending 20,000 rifles to Ireland to stir unrest in Britain. The UK government placed Ireland under in response to the Easter Rising, though once the immediate threat of revolution had dissipated, the authorities did try to make concessions to nationalist feeling. However, opposition to involvement in the war increased in Ireland, resulting in the.

Other opposition came from s—some socialist, some religious—who refused to fight. In Britain, 16,000 people asked for conscientious objector status. Some of them, most notably prominent peace activist, refused both military and. Many suffered years of prison, including and bread and water diets. Even after the war, in Britain many job advertisements were marked "No conscientious objectors need apply".

The started in the summer of 1916, when the Russian Empire government ended its exemption of Muslims from military service.

In 1917, a series of French Army Mutinies led to dozens of soldiers being executed and many more imprisoned.

On 1–4 May 1917, about 100,000 workers and soldiers of, and after them, the workers and soldiers of other Russian cities, led by the Bolsheviks, demonstrated under banners reading "Down with the war!" and "all power to the soviets!" The mass demonstrations resulted in a crisis for the. In, in May 1917, Bolshevik revolutionaries organised and engaged in rioting calling for an end to the war, and managed to close down factories and stop public transportation. The Italian army was forced to enter Milan with tanks and machine guns to face Bolsheviks and, who fought violently until 23 May when the army gained control of the city. Almost 50 people (including three Italian soldiers) were killed and over 800 people arrested.

In September 1917, began questioning why they were fighting for the French at all and mutinied. In Russia, opposition to the war led to soldiers also establishing their own revolutionary committees, which helped foment the, with the call going up for "bread, land, and peace". The, written by Vladimir Lenin, was passed on 8November 1917, following the success of the October Revolution. The Bolsheviks agreed to a peace treaty with Germany, the, despite its harsh conditions. The led to the abdication of the Kaiser and German surrender.

Conscription
Conscription was common in most European countries. However, it was controversial in English-speaking countries. It was especially unpopular among minority ethnic groups—especially the Irish Catholics in Ireland and Australia, and the French Catholics in Canada.

Canada
In Canada the issue produced. It opened a political gap between s, who believed their true loyalty was to Canada and not to the British Empire, and members of the Anglophone majority, who saw the war as a duty to their British heritage.

Australia
Australia had a form of conscription at the outbreak of the war, as compulsory military training had been introduced in 1911. However, the Defence Act 1903 provided that unexempted males could be called upon only for home defence during times of war, not overseas service. Prime Minister Billy Hughes wished to amend the legislation to require conscripts to serve overseas, and held two non-binding referendums – and  – in order to secure public support. Both were defeated by narrow margins, with farmers, the, the Catholic Church, and Irish-Australians combining to campaign for the "No" vote. The issue of conscription caused the. Hughes and his supporters were expelled from the party, forming the and then the. Despite the referendum results, the Nationalists won a landslide victory at the.

Britain
In Britain, conscription resulted in the calling up of nearly every physically fit man in Britain—six of ten million eligible. Of these, about 750,000 lost their lives. Most deaths were those of young unmarried men; however, 160,000 wives lost husbands and 300,000 children lost fathers. Conscription during the First World War began when the British government passed the in 1916. The act specified that single men aged 18 to 40 years old were liable to be called up for military service unless they were widowed with children or ministers of a religion. There was a system of to adjudicate upon claims for exemption upon the grounds of performing civilian work of national importance, domestic hardship, health, and conscientious objection. The law went through several changes before the war ended. Married men were exempt in the original Act, although this was changed in June 1916. The age limit was also eventually raised to 51 years old. Recognition of work of national importance also diminished, and in the last year of the war there was some support for the conscription of clergy. Conscription lasted until mid-1919. Due to the political situation in Ireland, conscription was never applied there; only in, and.

United States
In the United States, conscription began in 1917 and was generally well received, with a few pockets of opposition in isolated rural areas. The administration decided to rely primarily on conscription, rather than voluntary enlistment, to raise military manpower for when only 73,000 volunteers enlisted out of the initial 1million target in the first six weeks of the war. In 1917 10 million men were registered. This was deemed to be inadequate, so age ranges were increased and exemptions reduced, and so by the end of 1918 this increased to 24 million men that were registered with nearly 3million inducted into the military services. The draft was universal and included blacks on the same terms as whites, although they served in different units. In all 367,710 black Americans were drafted (13% of the total), compared to 2,442,586 white (87%).

Forms of resistance ranged from peaceful protest to violent demonstrations and from humble letter-writing campaigns asking for mercy to radical newspapers demanding reform. The most common tactics were dodging and desertion, and many communities sheltered and defended their draft dodgers as political heroes. Many socialists were jailed for "obstructing the recruitment or enlistment service". The most famous was Eugene Debs, head of the Socialist Party of America, who ran for president in 1920 from his prison cell. In 1917 a number of radicals and anarchists challenged the new draft law in federal court, arguing that it was a direct violation of the Thirteenth Amendment's prohibition against slavery and involuntary servitude. The Supreme Court unanimously upheld the constitutionality of the draft act in the on 7January 1918.

Austria-Hungary
Like all the armies of mainland Europe, Austria-Hungary relied on conscription to fill its ranks. Officer recruitment, however, was voluntary. The effect of this at the start of the war was that well over a quarter of the rank and file were Slavs, while more than 75% of the officers were ethnic Germans. This was much resented. The army has been described as being "run on colonial lines" and the Slav soldiers as "disaffected". Thus conscription contributed greatly to Austria's disastrous performance on the battlefield.

Diplomacy
The non-military diplomatic and propaganda interactions among the nations were designed to build support for the cause, or to undermine support for the enemy. For the most part, wartime diplomacy focused on five issues: ; defining and redefining the war goals, which became harsher as the war went on; luring neutral nations (Italy, Ottoman Empire, Bulgaria, Romania) into the coalition by offering slices of enemy territory; and encouragement by the Allies of nationalistic minority movements inside the Central Powers, especially among Czechs, Poles, and Arabs. In addition, there were multiple peace proposals coming from neutrals, or one side or the other; none of them progressed very far.

Legacy and memory
"... "Strange, friend," I said, "Here is no cause to mourn." "None," said the other, "Save the undone years"..."

-, Strange Meeting, 1918

"The War was an unprecedented triumph for natural science. [ ] Bacon had promised that knowledge would be power, and power it was: power to destroy the bodies and souls of men more rapidly than had ever been done by human agency before. This triumph paved the way to other triumphs: improvements in transport, in sanitation, in surgery, medicine, and psychiatry, in commerce and industry, and, above all, in preparations for the next war."

-, writing in 1939.

The first tentative efforts to comprehend the meaning and consequences of modern warfare began during the initial phases of the war, and this process continued throughout and after the end of hostilities, and is still underway, more than a century later.

Historiography
Historian Heather Jones argues that the has been reinvigorated by the cultural turn in recent years. Scholars have raised entirely new questions regarding military occupation, radicalisation of politics, race, and the male body. Furthermore, new research has revised our understanding of five major topics that historians have long debated: Why the war began, why the Allies won, whether generals were responsible for high casualty rates, how the soldiers endured the horrors of trench warfare, and to what extent the civilian homefront accepted and endorsed the war effort.

Memorials
Memorials were erected in thousands of villages and towns. Close to battlefields, those buried in improvised burial grounds were gradually moved to formal graveyards under the care of organisations such as the, the , the , and. Many of these graveyards also have central monuments to the missing or dead, such as the  memorial and the.

In 1915, a Canadian army doctor, wrote the poem  as a salute to those who perished in the Great War. Published in on 8December 1915, it is still recited today, especially on  and.

in, is a memorial dedicated to all Americans who served in World WarI. The was dedicated on 1November 1921, when the supreme Allied commanders spoke to a crowd of more than 100,000 people.

The UK Government has budgeted substantial resources to. The lead body is the. On 3August 2014, French President and German President  together marked  by laying the first stone of a memorial in Vieil Armand, known in German as, for French and German soldiers killed in the war.

Cultural memory
World War I had a lasting impact on. It was seen by many in Britain as signalling the end of an era of stability stretching back to the, and across Europe many regarded it as a watershed. Historian explained:

"A generation of innocent young men, their heads full of high abstractions like Honour, Glory and England, went off to war to make the world safe for democracy. They were slaughtered in stupid battles planned by stupid generals. Those who survived were shocked, disillusioned and embittered by their war experiences, and saw that their real enemies were not the Germans, but the old men at home who had lied to them. They rejected the values of the society that had sent them to war, and in doing so separated their own generation from the past and from their cultural inheritance."

This has become the most common perception of World War I, perpetuated by the art, cinema, poems, and stories published subsequently. Films such as ', ' and ' have perpetuated the idea, while war-time films including Camrades, ', and  indicate that the most contemporary views of the war were overall far more positive. Likewise, the art of, , , and in Britain painted a negative view of the conflict in keeping with the growing perception, while popular war-time artists such as  painted more serene and pleasant interpretations subsequently rejected as inaccurate. Several historians like, and  have challenged these interpretations as partial and al views:

"These beliefs did not become widely shared because they offered the only accurate interpretation of wartime events. In every respect, the war was much more complicated than they suggest. In recent years, historians have argued persuasively against almost every popular cliché of World WarI. It has been pointed out that, although the losses were devastating, their greatest impact was socially and geographically limited. The many emotions other than horror experienced by soldiers in and out of the front line, including comradeship, boredom, and even enjoyment, have been recognised. The war is not now seen as a 'fight about nothing', but as a war of ideals, a struggle between aggressive militarism and more or less liberal democracy. It has been acknowledged that British generals were often capable men facing difficult challenges, and that it was under their command that the British army played a major part in the defeat of the Germans in 1918: a great forgotten victory."

Though these views have been discounted as "myths", they are common. They have dynamically changed according to contemporary influences, reflecting in the 1950s perceptions of the war as "aimless" following the contrasting Second World War and emphasising conflict within the ranks during times of class conflict in the 1960s. The majority of additions to the contrary are often rejected.

Social trauma
The social trauma caused by unprecedented rates of casualties manifested itself in different ways, which have been the subject of subsequent historical debate.

The of  was destroyed, and those who had fought in the war were referred to as the. For years afterwards, people mourned the dead, the missing, and the many disabled. Many soldiers returned with severe trauma, suffering from (also called neurasthenia, a condition related to ). Many more returned home with few after-effects; however, their silence about the war contributed to the conflict's growing mythological status. Though many participants did not share in the experiences of combat or spend any significant time at the front, or had positive memories of their service, the images of suffering and trauma became the widely shared perception. Such historians as Dan Todman,, and Samuel Heyns have all published works since the 1990s arguing that these common perceptions of the war are factually incorrect.

Discontent in Germany
The rise of and  included a revival of the nationalist spirit and a rejection of many post-war changes. Similarly, the popularity of the stab-in-the-back legend (German: Dolchstoßlegende) was a testament to the psychological state of defeated Germany and was a rejection of responsibility for the conflict. This conspiracy theory of betrayal became common, and the German populace came to see themselves as victims. The widespread acceptance of the "stab-in-the-back" theory delegitimised the Weimar government and destabilised the system, opening it to extremes of right and left.

Communist and fascist movements around Europe drew strength from this theory and enjoyed a new level of popularity. These feelings were most pronounced in areas directly or harshly affected by the war. was able to gain popularity by using German discontent with the still controversial Treaty of Versailles. World WarII was in part a continuation of the power struggle never fully resolved by World WarI. Furthermore, it was common for Germans in the 1930s to justify acts of aggression due to perceived injustices imposed by the victors of World WarI. American historian wrote that:

"The 'Age of Totalitarianism' included nearly all the infamous examples of genocide in modern history, headed by the Jewish Holocaust, but also comprising the mass murders and purges of the Communist world, other mass killings carried out by Nazi Germany and its allies, and also the Armenian Genocide of 1915. All these slaughters, it is argued here, had a common origin, the collapse of the elite structure and normal modes of government of much of central, eastern and southern Europe as a result of World WarI, without which surely neither Communism nor Fascism would have existed except in the minds of unknown agitators and crackpots."

Economic effects
One of the most dramatic effects of the war was the expansion of governmental powers and responsibilities in Britain, France, the United States, and the Dominions of the British Empire. To harness all the power of their societies, governments created new ministries and powers. New taxes were levied and laws enacted, all designed to bolster the ; many have lasted to this day. Similarly, the war strained the abilities of some formerly large and bureaucratised governments, such as in Austria-Hungary and Germany.

(GDP) increased for three Allies (Britain, Italy, and the United States), but decreased in France and Russia, in neutral Netherlands, and in the three main Central Powers. The shrinkage in GDP in Austria, Russia, France, and the Ottoman Empire ranged between 30% and 40%. In Austria, for example, most pigs were slaughtered, so at war's end there was no meat.

In all nations, the government's share of GDP increased, surpassing 50% in both Germany and France and nearly reaching that level in Britain. To pay for purchases in the United States, Britain cashed in its extensive investments in American railroads and then began borrowing heavily from. President Wilson was on the verge of cutting off the loans in late 1916, but allowed a great increase in lending to the Allies. After 1919, the US demanded repayment of these loans. The repayments were, in part, funded by German reparations that, in turn, were supported by American loans to Germany. This circular system collapsed in 1931 and some loans were never repaid. Britain still owed the United States $4.4 of World WarI debt in 1934, the last instalment was finally paid in 2015.

Macro- and micro-economic consequences devolved from the war. Families were altered by the departure of many men. With the death or absence of the primary wage earner, women were forced into the workforce in unprecedented numbers. At the same time, industry needed to replace the lost labourers sent to war. This aided the struggle for.

World War I further compounded the gender imbalance, adding to the phenomenon of. The deaths of nearly one million men during the war in Britain increased the gender gap by almost a million: from 670,000 to 1,700,000. The number of unmarried women seeking economic means grew dramatically. In addition, demobilisation and economic decline following the war caused high unemployment. The war increased female employment; however, the return of demobilised men displaced many from the workforce, as did the closure of many of the wartime factories.

In Britain, rationing was finally imposed in early 1918, limited to meat, sugar, and fats (butter and margarine), but not bread. The new system worked smoothly. From 1914 to 1918, trade union membership doubled, from a little over four million to a little over eight million.

Britain turned to her colonies for help in obtaining essential war materials whose supply from traditional sources had become difficult. Geologists such as were called on to find new resources of precious minerals in the African colonies. Kitson discovered important new deposits of, used in munitions production, in the.

Article 231 of the Treaty of Versailles (the so-called "war guilt" clause) stated Germany accepted responsibility for "all the loss and damage to which the Allied and Associated Governments and their nationals have been subjected as a consequence of the war imposed upon them by the aggression of Germany and her allies." It was worded as such to lay a legal basis for reparations, and a similar clause was inserted in the treaties with Austria and Hungary. However neither of them interpreted it as an admission of war guilt." In 1921, the total reparation sum was placed at 132 billion gold marks. However, "Allied experts knew that Germany could not pay" this sum. The total sum was divided into three categories, with the third being "deliberately designed to be chimerical" and its "primary function was to mislead public opinion ... into believing the "total sum was being maintained." Thus, 50 billion gold marks (12.5 billion dollars) "represented the actual Allied assessment of German capacity to pay" and "therefore ... represented the total German reparations" figure that had to be paid.

This figure could be paid in cash or in kind (coal, timber, chemical dyes, etc.). In addition, some of the territory lost—via the treaty of Versailles—was credited towards the reparation figure as were other acts such as helping to restore the Library of Louvain. By 1929, the arrived, causing political chaos throughout the world. In 1932 the payment of reparations was suspended by the international community, by which point Germany had paid only the equivalent of 20.598 billion gold marks in reparations. With the rise of Adolf Hitler, all bonds and loans that had been issued and taken out during the 1920s and early 1930s were cancelled. notes "refusing to pay doesn't make an agreement null and void. The bonds, the agreement, still exist." Thus, following the Second World War, at the in 1953, Germany agreed to resume payment on the money borrowed. On 3October 2010, Germany made the final payment on these bonds.

The war contributed to the evolution of the from women's jewellery to a practical everyday item, replacing the, which requires a free hand to operate. Military funding of advancements in radio contributed to the postwar popularity of the medium.

Animated maps

 * "Europe plunges into war"
 * Europe at the end of the war