World War I World War I ( WWI ) , also known as the First World War , was a global war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918 . From the time of its occurrence until the approach of World War II in 1939 , it was called simply the World War or the Great War , and thereafter the First World War or World War I . In America it was initially called the European War . More than 9 million combatants were killed : a scale of death impacted by industrial advancements , geographic stalemate and reliance on human wave attack s . It was the fifth - deadliest conflict in world history , paving the way for major political changes , including revolutions in many of the nations involved . The war drew in all the world ' s economic great power s , which were assembled in two opposing alliances : the Allies ( based on the Triple Entente of the United Kingdom , France and the Russian Empire ) and the Central Powers of Germany and Austria - Hungary . Although Italy had also been a member of the Triple Alliance alongside Germany and Austria - Hungary , it did not join the Central Powers , as Austria - Hungary had taken the offensive against the terms of the alliance . These alliances were both reorganised and expanded as more nations entered the war : Italy , Japan and the United States joined the Allies , and the Ottoman Empire and Bulgaria the Central Powers . Ultimately , more than 70 million military personnel , including 60 million Europeans , were mobilised in one of the largest wars in history . Although a resurgence of imperialism was an underlying cause , the immediate trigger for war was the 28 June 1914 assassination of Archduke Franz Ferdinand of Austria , heir to the throne of Austria - Hungary , by Yugoslav nationalist Gavrilo Princip in Sarajevo . This set off a diplomatic crisis when Austria - Hungary delivered an ultimatum to the Kingdom of Serbia , and international alliances formed over the previous decades were invoked . Within weeks , the major powers were at war and the conflict soon spread around the world . On 28 July , the Austro - Hungarians fired the first shots in preparation for the invasion of Serbia . As Russia mobilised , Germany invaded neutral Belgium and Luxembourg before moving towards France , leading Britain to declare war on Germany . After the German march on Paris was brought to a halt , what became known as the Western Front settled into a battle of attrition , with a trench line that would change little until 1917 . Meanwhile , on the Eastern Front , the Russian army was successful against the Austro - Hungarians , but was stopped in its invasion of East Prussia by the Germans . In November 1914 , the Ottoman Empire joined the war , opening fronts in the Caucasus , Mesopotamia and the Sinai . Italy and Bulgaria went to war in 1915 and Romania in 1916 . The war approached a resolution after the Russian Tsar ' s government collapsed in March 1917 and a subsequent revolution in November brought the Russians to terms with the Central Powers . After a 1918 German offensive along the western front , the Allies drove back the Germans in a series of successful offensives and American forces began entering the trenches . Germany , which had its own trouble with revolutionaries , agreed to an armistice on 11 November 1918 , ending the war in victory for the Allies . By the end of the war , four major imperial powers — the German , Russian , Austro - Hungarian and Ottoman empires — ceased to exist . The successor states of the former two lost substantial territory , while the latter two were dismantled . The map of Europe was redrawn , with several independent nations restored or created . The League of Nations formed with the aim of preventing any repetition of such an appalling conflict . This aim failed , with weakened states , renewed European nationalism and the humiliation of Germany contributing to the rise of fascism and the conditions for World War II . Names . In Canada , " Maclean ' s Magazine " in October 1914 said , " Some wars name themselves . This is the Great War . " A history of the origins and early months of the war published in New York in late 1914 was titled " The World War " . During the Interwar period , the war was most often called the " World War " and the " Great War " in English - speaking countries . After the onset of the Second World War in 1939 , the terms " World War I " or " the First World War " became standard , with British and Canadian historians favouring the " First World War " , and Americans " World War I " . The term " First World War " was first used in September 1914 by the German philosopher Ernst Haeckel , 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 . " " The First World War " was also the title of a 1920 history by the officer and journalist Charles à Court Repington . Background . In the 19th Century , the major European powers had gone to great lengths to maintain a balance of power throughout Europe , resulting in the existence of a complex network of political and military alliances throughout the continent by 1900 . These had started in 1815 , with the Holy Alliance between Prussia , Russia , and Austria . Then , in October 1873 , German Chancellor Otto von Bismarck negotiated the League of the Three Emperors ( German : " Dreikaiserbund " ) between the monarchs of Austria - Hungary , Russia and Germany . This agreement failed because Austria - Hungary and Russia could not agree over Balkan policy , leaving Germany and Austria - Hungary in an alliance formed in 1879 , called the Dual Alliance . This was seen as a method of countering Russian influence in the Balkans as the Ottoman Empire continued to weaken . In 1882 , this alliance was expanded to include Italy in what became the Triple Alliance . Bismarck had especially worked to hold Russia at Germany ' s side to avoid a two - front war with France and Russia . When Wilhelm II ascended to the throne as German Emperor ( " Kaiser " ) , Bismarck was compelled to retire and his system of alliances was gradually de - emphasised . For example , the Kaiser refused to renew the Reinsurance Treaty with Russia in 1890 . Two years later , the Franco - Russian Alliance was signed to counteract the force of the Triple Alliance . In 1904 , Britain signed a series of agreements with France , the Entente Cordiale , and in 1907 , Britain and Russia signed the Anglo - Russian Convention . While these agreements did not formally ally Britain with France or Russia , they made British entry into any future conflict involving France or Russia a possibility , and the system of interlocking bilateral agreements became known as the Triple Entente . German industrial and economic power had grown greatly after unification and the foundation of the Empire in 1871 . From the mid - 1890s on , the government of Wilhelm II used this base to devote significant economic resources for building up the " Kaiserliche Marine " ( Imperial German Navy ) , established by Admiral Alfred von Tirpitz , in rivalry with the British Royal Navy for world naval supremacy . As a result , each nation strove to out - build the other in terms of capital ship s . With the launch of in 1906 , the British Empire expanded on its significant advantage over its German rival . The arms race between Britain and Germany eventually extended to the rest of Europe , with all the major powers devoting their industrial base to producing the equipment and weapons necessary for a pan - European conflict . Between 1908 and 1913 , the military spending of the European powers increased by 50 % . Austria - Hungary precipitated the Bosnian crisis of 1908 – 1909 by officially annexing the former Ottoman territory of Bosnia and Herzegovina , which it had occupied since 1878 . This angered the Kingdom of Serbia and its patron , the Pan - Slavic and Orthodox Russian Empire . Russian political manoeuvring in the region destabilised peace accords , which were already fracturing in what was known as " the powder keg of Europe " . In 1912 and 1913 , the First Balkan War was fought between the Balkan League and the fracturing Ottoman Empire . The resulting Treaty of London further shrank the Ottoman Empire , creating an independent Albanian State while enlarging the territorial holdings of Bulgaria , Serbia , Montenegro , and Greece . When Bulgaria attacked both Serbia and Greece on 16 June 1913 , it lost most of Macedonia to Serbia and Greece and Southern Dobruja to Romania in the 33 - day Second Balkan War , further destabilising the region . July 1914 crisis . On 28 June 1914 , Gavrilo Princip , a Bosnian Serb student and member of Young Bosnia , assassinated the heir to the Austro - Hungarian throne , Archduke Franz Ferdinand of Austria , in Sarajevo , Bosnia . This began a month of diplomatic manoeuvring between Austria - Hungary , Germany , Russia , France , and Britain called the July Crisis . Believing correctly that Serbian officials ( especially the officers of the Black Hand ) were involved in the plot , and wanting to finally end Serbian interference in Bosnia , Austria - Hungary delivered to Serbia the July Ultimatum , a series of ten demands intentionally made unacceptable , intending to provoke a war with Serbia . When Serbia agreed to only eight of the ten demands , Austria - Hungary declared war on 28 July 1914 . Strachan argues , " Whether an equivocal and early response by Serbia would have made any difference to Austria - Hungary ' s behaviour must be doubtful . Franz Ferdinand was not the sort of personality who commanded popularity , and his demise did not cast the empire into deepest mourning " . The Russian Empire , unwilling to allow Austria - Hungary to eliminate its influence in the Balkans , and in support of its longtime Serb protégé , ordered a partial mobilisation one day later . Germany mobilised on 30 July . Germany ' s war plan , the Schlieffen Plan , relied on a quick , massive invasion of France to eliminate the threat on the West , before turning east against Russia . Simultaneously with its mobilisation against Russia , therefore , the German government issued demands that France remain neutral . The French cabinet resisted military pressure to commence immediate mobilisation , and ordered its troops to withdraw from the border to avoid any incident . France only mobilised on the evening of 2 August , when Germany invaded Belgium and attacked French troops . Germany declared war on Russia on the same day . Britain declared war on Germany on 4 August 1914 , following an " unsatisfactory reply " to the British ultimatum that Belgium must be kept neutral . Progress of the war . Opening hostilities . 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 the replacements 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 Austro - Hungarian Army to divide its forces between the Russian and Serbian fronts . On 9 September 1914 , the " Septemberprogramm " , a possible plan that detailed Germany ' s specific war aims and the conditions that Germany sought to force on the Allied Powers , was outlined by the , Theobald von Bethmann - Hollweg . It was never officially adopted . Serbian campaign . Austria invaded and fought the Serbian army at the Battle of Cer and Battle of Kolubara 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 sizable forces on the Serbian front , weakening its efforts against Russia . Serbia ' s defeat of the Austro - Hungarian invasion of 1914 counts among the major upset victories of the last century . German forces in Belgium and France . At the outbreak of World War I , the German army ( consisting in the West of seven field armies ) carried out a modified version of the Schlieffen Plan . This marched German armies through neutral Belgium and into France , before turning southwards to encircle the French army on the German border . Since France had declared that it would " keep full freedom of acting in case of a war between Germany and Russia " , Germany had to expect the possibility of an attack by France on one front and by Russia on the other . To meet such a scenario , the Schlieffen Plan stated that Germany must try to defeat France quickly ( as had happened in the Franco - Prussian War of 1870 – 71 ) . It further suggested that to repeat a fast victory in the west , Germany should not attack through the difficult terrain of Alsace - Lorraine ( which had a direct border west of the river Rhine ) , instead , the idea was to try to quickly cut Paris off from the English Channel and British assistance , and take Paris , thus winning the war . Then the armies would be moved over to the east to meet Russia . Russia was believed to need a long period of mobilisation before they could become a real threat to the Central Powers . The only existing German plan for " any " war had German armies marching through Belgium . Germany wanted free escort through Belgium ( and originally the Netherlands as well , which plan Kaiser Wilhelm II rejected ) to invade France . Neutral Belgium rejected this idea , so the Germans decided to invade through Belgium instead . France also wanted to move their troops into Belgium , but Belgium originally rejected this " suggestion " as well , in the hope of avoiding any war on Belgian soil . In the end , after the German invasion , Belgium did try to join their army with the French ( but a large part of the Belgian army retreated to Antwerp where they were forced to surrender when all hope of help was gone ) . The plan called for the right flank of the German advance to bypass the French armies ( which were concentrated on the Franco - German border , leaving the Belgian border without significant French forces ) and move south to Paris . Initially the Germans were successful , particularly in the Battle of the Frontiers ( 14 – 24 August ) . By 12 September , the French , with assistance from the British forces , halted the German advance east of Paris at the First Battle of the Marne ( 5 – 12 September ) , and pushed the German forces back some . The last days of this battle signified the end of mobile warfare in the west . The French offensive into Southern Alsace , launched on 20 August with the Battle of Mulhouse , had limited success . In the east , the Russians invaded with two armies , surprising the German staff who had not expected the Russians to move so early . A field army , the 8th , was rapidly moved from its previous role as reserve for the invasion of France , to East Prussia by rail across the German Empire . This army , led by general Paul von Hindenburg defeated Russia in a series of battles collectively known as the First Battle of Tannenberg ( 17 August – 2 September ) . But the failed Russian invasion , causing the fresh German troops to move to the east , allowed the tactical Allied victory at the First Battle of the Marne . The Central Powers were denied a quick victory in France and forced to fight a war on two fronts . The German army had fought its way into a good defensive position inside France and had permanently incapacitated 230 , 000 more French and British troops than it had lost itself . Despite this , communications problems and questionable command decisions cost Germany the chance of early victory . Asia and the Pacific . New Zealand occupied German Samoa ( later Western Samoa ) on 30 August 1914 . On 11 September , the Australian Naval and Military Expeditionary Force landed on the island of Neu Pommern ( later New Britain ) , which formed part of German New Guinea . On 28 October , the cruiser " SMS Emden " sank the Russian cruiser Zhemchug in the Battle of Penang . Japan seized Germany ' s Micronesian colonies and , after the Siege of Tsingtao , the German coaling port of Qingdao in the Chinese Shandong peninsula . As Vienna refused to withdraw the Austro - Hungarian cruiser " Kaiserin Elisabeth " from Tsingtao , Japan declared war not only on Germany , but also on Austria - Hungary ; the ship participated in the defense 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 7 August , French and British troops invaded the German protectorate of Togoland . On 10 August , German forces in South - West Africa attacked South Africa ; sporadic and fierce fighting continued for the rest of the war . The German colonial forces in German East Africa , led by Colonel Paul von Lettow - Vorbeck , fought a guerrilla warfare campaign during World War I and only surrendered two weeks after the armistice took effect in Europe . Indian support for the Allies . 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 Indian National Congress 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 Indian Home Rule . The Indian Army 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 both the central government and the princely state 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 War I . 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 the campaign for full independence that would be led by Mohandas Karamchand Gandhi and others . Western Front . Trench warfare begins ( 1914 – 1915 ) . Military tactics before World War I had failed to keep pace with advances in technology . These advances allowed for impressive defence systems , which out - of - date military tactics could not break through for most of the war . Barbed wire was a significant hindrance to massed infantry advances . Artillery , vastly more lethal than in the 1870s , coupled with machine gun s , made crossing open ground extremely difficult . Commanders on both sides failed to develop tactics for breaching entrenched positions without heavy casualties . In time , however , technology began to produce new offensive weapons , such as gas warfare and the tank . After the First Battle of the Marne ( 5 – 12 September 1914 ) , both Entente and German forces began a series of outflanking manoeuvres , in the so - called " Race to the Sea " . Britain and France soon found themselves facing an uninterrupted line of entrenched German forces from Lorraine to Belgium ' s coast . Britain and France sought to take the offensive , while Germany defended the occupied territories . Consequently , German trenches were much better constructed than those of their enemy ; Anglo - French trenches were only intended to be " temporary " before their forces broke through German defences . Both sides tried to break the stalemate using scientific and technological advances . On 22 April 1915 , at the Second Battle of Ypres , the Germans ( violating the Hague Convention ) used chlorine 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 first used in combat by the British during the Battle of Flers - Courcelette ( part of the wider Somme offensive ) on 15 September 1916 , with only partial success . However , their effectiveness would grow as the war progressed ; the Germans employed only very small numbers of their own design , supplemented by captured Allied tanks . Trench warfare continues ( 1916 – 1917 ) . 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 only mounted one major offensive , the Allies made several attempts to break through the German lines . In February 1916 the Germans attacked the French defensive positions at Verdun . Running until December 1916 , the battle saw initial German gains , before French counterattacks 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 Battle of the Somme was an Anglo - French offensive that ran from July to November 1916 . The opening of this offensive ( 1 July 1916 ) saw the British Army endure the bloodiest day in its history , suffering 57 , 470 casualties , including 19 , 240 dead , on the first day alone . 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 . 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 at frontal assault came at a high price for both the British and the French " poilu " and led to the widespread French Army Mutinies , after the failure of the costly Nivelle Offensive of April – May 1917 . The concurrent British Battle of Arras was more limited in scope , and more successful , although ultimately of little strategic value . A smaller part of the Arras offensive , the capture of Vimy Ridge by the Canadian Corps , 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 Passchendaele ( 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 . These years of trench warfare in the West saw 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 tactics constantly evolved to meet new battlefield challenges . Naval war . At the start of the war , the German Empire had cruiser s scattered across the globe , some of which were subsequently used to attack Allied merchant shipping . The British Royal Navy systematically hunted them down , though not without some embarrassment from its inability to protect Allied shipping . For example , the German detached light cruiser SMS " Emden " , part of the East - Asia squadron stationed at Qingdao , seized or destroyed 15 merchantmen , as well as sinking a Russian cruiser and a French destroyer . However , most of the German East - Asia squadron — consisting of the armoured cruisers and , light cruisers and 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 sank two armoured cruisers at the Battle of Coronel , but was almost destroyed at the Battle of the Falkland Islands in December 1914 , with only " Dresden " and a few auxiliaries escaping , but at the Battle of Más a Tierra these too were destroyed or interned . Soon after the outbreak of hostilities , Britain began a naval blockade of Germany . 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 , Germany expected a similar response to its unrestricted submarine warfare . The 1916 Battle of Jutland ( German : " Skagerrakschlacht " , or " Battle of the Skagerrak " ) developed into the largest naval battle of the war , the only full - scale clash of battleships during the war , and one of the largest in history . It took place on 31 May – 1 June 1916 , in the North Sea off Jutland . The Kaiserliche Marine ' s High Seas Fleet , commanded by Vice Admiral Reinhard Scheer , squared off against the Royal Navy ' s Grand Fleet , led by Admiral Sir John Jellicoe . The engagement was a stand off , as the Germans , outmanoeuvred by the larger British fleet , 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 U - boat s attempted to cut the supply lines between North America and Britain . The nature of submarine warfare 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 RMS " Lusitania " in 1915 , Germany promised not to target passenger liners , while Britain armed its merchant ships , placing them beyond the protection of the " cruiser rules " , which demanded warning and placing crews in " a place of safety " ( a standard that lifeboats did not meet ) . Finally , in early 1917 , Germany adopted a policy of unrestricted submarine warfare , realising that the Americans would eventually enter the war . Germany sought to strangle Allied sea lanes before the United States could transport a large army overseas , but could maintain only five long - range U - boats on station , to limited effect . The U - boat threat lessened in 1917 , when merchant ships began travelling in convoys , escorted by destroyer s . This tactic made it difficult for U - boats to find targets , which significantly lessened losses ; after the hydrophone and depth charge s were introduced , accompanying destroyers might 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 aircraft carrier s in combat , with launching Sopwith Camel s in a successful raid against the Zeppelin hangars at Tondern in July 1918 , as well as blimps for antisubmarine patrol . Southern theatres . War in the Balkans . Faced with Russia , Austria - Hungary could spare only one - third of its army to attack Serbia . After suffering heavy losses , the Austrians briefly occupied the Serbian capital , Belgrade . A Serbian counterattack in the battle of Kolubara , however , 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 Slovenia , Croatia and Bosnia provided troops for Austria - Hungary , invading Serbia as well as fighting Russia and Italy . Montenegro allied itself with Serbia . Serbia was conquered in a little more than a month , as the Central Powers , now including Bulgaria , sent in 600 , 000 troops . The Serbian army , fighting on two fronts and facing certain defeat , retreated into northern Albania ( which they had invaded at the beginning of the war ) . The Serbs suffered defeat in the Battle of Kosovo . Montenegro covered the Serbian retreat towards the Adriatic coast in the Battle of Mojkovac in 6 – 7 January 1916 , but ultimately the Austrians conquered Montenegro , too . 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 Salonica in Greece , to offer assistance and to pressure the government to declare war against the Central Powers . However , the pro - German King Constantine I dismissed the pro - Allied government of Eleftherios Venizelos before the Allied expeditionary force arrived . The friction between the King of Greece and the Allies continued to accumulate with the National Schism , 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 Athens between Allied and royalist forces ( an incident known as Noemvriana ) , the King of Greece resigned and his second son Alexander took his place ; Greece then officially joined the war on the side of the Allies . In the beginning , the Macedonian Front was mostly static . French and Serbian forces retook limited areas of Macedonia by recapturing Bitola on 19 November 1916 following the costly Monastir Offensive , which brought stabilization of the front . Serbian and French troops finally made a breakthrough in September 1918 , after most of the German and Austro - Hungarian troops had been withdrawn . The Bulgarians suffered their only defeat of the war at the Battle of Dobro Pole : Bulgaria capitulated two weeks 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 Budapest and Vienna was now opened to Allied forces . Hindenburg and Ludendorff concluded that the strategic and operational balance had now shifted decidedly against the Central Powers and , a day after the Bulgarian collapse , insisted on an immediate peace settlement . Ottoman Empire . The Ottoman Empire joined the Central Powers in the war , the secret Ottoman – German Alliance having been signed in August 1914 . It threatened Russia ' s Caucasian territories and Britain ' s communications with India " via " the Suez Canal . The British and French opened overseas fronts with the Gallipoli ( 1915 ) and Mesopotamian campaign s . In Gallipoli , the Ottoman Empire successfully repelled the British , French , and Australian and New Zealand Army Corps ( ANZACs ) . In Mesopotamia , by contrast , after the disastrous Siege of Kut ( 1915 – 16 ) , British Imperial forces reorganised and captured Baghdad in March 1917 . Further to the west , the Suez Canal was successfully defended from Ottoman attacks in 1915 and 1916 ; in August , a joint German and Ottoman force was defeated at the Battle of Romani by the ANZAC Mounted and the 52nd ( Lowland ) Infantry Division s . Following this victory , a British Empire Egyptian Expeditionary Force advanced across the Sinai Peninsula , pushing Ottoman forces back in the Battle of Magdhaba in December and the Battle of Rafa on the border between the Egyptian Sinai and Ottoman Palestine in January 1917 . Russian armies generally had the best of it in the Caucasus . Enver Pasha , 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 Battle of Sarikamish . General Yudenich , 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 Grand Duke Nicholas assumed command of the Caucasus front . Nicholas planned a railway from Russian Georgia 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 Czar abdicated in the course of the February Revolution and the Russian Caucasus Army began to fall apart . Instigated by the Arab bureau of the British Foreign Office , the Arab Revolt started with the help of Britain in June 1916 at the Battle of Mecca , led by Sherif Hussein of Mecca , and ended with the Ottoman surrender of Damascus . Fakhri Pasha , the Ottoman commander of Medina , resisted for more than two and half years during the Siege of Medina . Along the border of Italian Libya and British Egypt , the Senussi tribe , 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 Senussi Campaign . 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 Trentino , Istria , and Dalmatia . Rome had a secret 1902 pact with France , effectively nullifying its alliance . 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 Southern Tyrol , Julian March and territory on the Dalmatian coast after the defeat of Austria - Hungary . This was formalised by the Treaty of London . 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 . Italy ' s entry was engineered in secret by three individuals — the Prime Minister , Antonio Salandra , the Foreign Minister , Sidney Sonnino , and King Victor Emmanuel III . Militarily , the Italians had numerical superiority . This advantage , however , was lost , not only because of the difficult terrain in which fighting took place , but also because of the strategies and tactics employed . Field Marshal Luigi Cadorna , a staunch proponent of the frontal assault , had dreams of breaking into the Slovenian plateau , taking Ljubljana and threatening Vienna . Cadorna ' s plan did not take into account the difficulties of the rugged Alpine terrain , or the technological changes that created trench warfare , giving rise to a series of bloody and inconclusive stalemated offensives . 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 Kaiserschützen and engaged Italian Alpini in bitter hand - to - hand combat throughout the summer . The Austro - Hungarians counterattacked in the Altopiano of Asiago , towards Verona and Padua , in the spring of 1916 ( " Strafexpedition " ) , but made little progress . Beginning in 1915 , the Italians under Cadorna mounted eleven offensives on the Isonzo front along the Isonzo River , northeast of Trieste . All eleven offensives were repelled by the Austro - Hungarians , who held the higher ground . In the summer of 1916 , the Italians captured the town of Gorizia . After this minor victory , the front remained static for over a year , despite several Italian offensives . In the autumn of 1917 , thanks to the improving situation on the Eastern front , the Austro - Hungarian troops received large numbers of reinforcements , including German Stormtrooper s and the elite Alpenkorps . The Central Powers launched a crushing offensive on 26 October 1917 , spearheaded by the Germans . They achieved a victory at Caporetto . The Italian Army was routed and retreated more than to reorganise , stabilising the front at the Piave River . Since the Italian Army had suffered heavy losses in the Battle of Caporetto , the Italian Government called to arms the so - called " ' 99 Boys " ( " Ragazzi del ' 99 " ) : that is , all males who were 18 years old or older . In 1918 , the Austro - Hungarians failed to break through in a series of battles on the Piave River , and were finally decisively defeated in the Battle of Vittorio Veneto in October of that year . From 5 – 6 November 1918 , Italian forces were reported to have reached Lissa , Lagosta , Sebenico , and other localities on the Dalmatian coast . By the end of hostilities in November 1918 , the Italian military had seized control of the entire portion of Dalmatia that had been guaranteed to Italy by the London Pact . In 1918 , Admiral Enrico Millo declared himself Italy ' s Governor of Dalmatia . Austria - Hungary surrendered in early 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 . When the Entente Powers promised Romania large territories of eastern Hungary ( Transylvania and Banat ) , which had a large Romanian population , in exchange for Romania ' s declaring war on the Central Powers , the Romanian government renounced its neutrality and , on 27 August 1916 , the Romanian Army launched an attack against Austria - Hungary , with limited Russian support . The Romanian offensive was initially successful , pushing back the Austro - Hungarian troops in Transylvania , but a counterattack by the forces of the Central Powers drove back the Russo - Romanian forces . As a result of the Battle of Bucharest , the Central Powers occupied Bucharest on 6 December 1916 . Fighting in Moldova continued in 1917 , resulting in a costly stalemate for the Central Powers . Russian withdrawal from the war in late 1917 as a result of the October Revolution meant that Romania was forced to sign an armistice with the Central Powers on 9 December 1917 . In January 1918 , Romanian forces established control over Bessarabia as the Russian Army abandoned the province . Although a treaty was signed by the Romanian and the Bolshevik Russian government following talks from 5 – 9 March 1918 on the withdrawal of Romanian forces from Bessarabia within two months , on 27 March 1918 Romania attached Bessarabia to its territory , formally based on a resolution passed by the local assembly of the territory on the unification with Romania . Romania officially made peace with the Central Powers by signing the Treaty of Bucharest on 7 May 1918 . Under that 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 Carpathian Mountains , and 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 Alexandru Marghiloman government , and Romania nominally re - entered the war on 10 November 1918 . The next day , the Treaty of Bucharest was nullified by the terms of the Armistice of Compiègne . Total Romanian deaths from 1914 to 1918 , military and civilian , within contemporary borders , were estimated at 748 , 000 . Eastern Front . Initial actions . While the Western Front had reached stalemate , the war continued in East Europe . Initial Russian plans called for simultaneous invasions of Austrian Galicia and German East Prussia . Although Russia ' s initial advance into Galicia was largely successful , it was driven back from East Prussia by Hindenburg and Ludendorff at Tannenberg and the Masurian Lakes in August and September 1914 . Russia ' s less developed industrial base and ineffective military leadership was 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 . On 5 August , they captured Warsaw and forced the Russians to withdraw from Poland . Russian Revolution . Despite the success of the June 1916 Brusilov Offensive in eastern Galicia , dissatisfaction with the Russian government ' s conduct of the war grew . The offensive ' s success was undermined by the reluctance of other generals to commit their forces to support the victory . Allied and Russian forces were revived only temporarily by Romania ' s entry into the war on 27 August . German forces came to the aid of embattled Austro - Hungarian units in Transylvania , and Bucharest fell to the Central Powers on 6 December . Meanwhile , unrest grew in Russia , as the Tsar remained at the front . Empress Alexandra ' s increasingly incompetent rule drew protests and resulted in the murder of her favourite , Rasputin , at the end of 1916 . In March 1917 , demonstrations in Petrograd culminated in the abdication of Tsar Nicholas II and the appointment of a weak Provisional Government , which shared power with the Petrograd Soviet socialists . This arrangement led to confusion and chaos both at the front and at home . The army became increasingly ineffective . Discontent and the weaknesses of the Provisional Government led to a rise in the popularity of the Bolshevik Party , led by Vladimir Lenin , which demanded an immediate end to the war . The successful armed uprising by the Bolsheviks 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 the Ukraine unopposed , the new government acceded to the Treaty of Brest - Litovsk on 3 March 1918 . The treaty ceded vast territories , including Finland , the Baltic provinces , parts of Poland and Ukraine to the Central Powers . Despite this enormous apparent German success , the manpower required for German occupation of former Russian territory may have contributed to the failure of the Spring Offensive and secured relatively little food or other materiel . With the adoption of the Treaty of Brest - Litovsk , the Entente no longer existed . The Allied powers led a small - scale invasion of Russia , partly to stop Germany from exploiting Russian resources and , to a lesser extent , to support the " Whites " ( as opposed to the " Reds " ) in the Russian Civil War . Allied troops landed in Arkhangelsk and in Vladivostok as part of the North Russia Intervention . Central Powers proposal for starting peace negotiations . In December 1916 , after ten brutal months of the Battle of Verdun and a successful offensive against Romania , the Germans attempted to negotiate a peace with the Allies . Soon after , the U . S . president , Woodrow Wilson , attempted to intervene as a peacemaker , asking in a note for both sides to state their demands . Lloyd George ' s 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 , because Germany did not state any specific proposals . To Wilson , the Entente powers stated that they would not start peace negotiations until the Central powers evacuated all occupied Allied territories and provided indemnities for all damage which had been done . 1917 – 1918 . Developments in 1917 . Events of 1917 proved decisive in ending the war , although their effects were not fully felt until 1918 . The British naval blockade began to have a serious impact on Germany . In response , in February 1917 , the German General Staff convinced Chancellor 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 5 to 6 months , before American intervention could make an impact . In reality , 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 convoy system became extremely effective in reducing the U - boat threat . Britain was safe from starvation , while German industrial output fell and the United States troops joined the war in large numbers far earlier than Germany had anticipated . On 3 May 1917 , during the Nivelle Offensive , the weary French 2nd Colonial Division , veterans of the Battle of Verdun , refused their orders , arriving drunk and without their weapons . Their officers lacked the means to punish an entire division , and harsh measures were not immediately implemented . Then , the French Army Mutinies afflicted an additional 54 French divisions and saw 20 , 000 men desert . The other Allied forces attacked , but sustained tremendous casualties . 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 . Robert Nivelle was removed from command by 15 May , replaced by General Philippe Pétain , who suspended bloody large - scale attacks . The victory of Austria - Hungary and Germany at the Battle of Caporetto led the Allies to convene the Rapallo Conference at which they formed the Supreme War Council to coordinate planning . Previously , British and French armies had operated under separate commands . In December , the Central Powers signed an armistice with Russia . This released 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 , the leaders of the Central Powers and the Allies became increasingly fearful of social unrest and revolution in Europe . Thus , both sides urgently sought a decisive victory . In 1917 , Emperor Charles I of Austria secretly attempted separate peace negotiations with Clemenceau , with his wife ' s brother Sixtus 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 First and Second Battles of Gaza , German and Ottoman forces stopped the advance of the Egyptian Expeditionary Force , which had begun in August 1916 at Romani . At the end of October , the Sinai and Palestine Campaign resumed , when General Edmund Allenby ' s XXth Corps , XXI Corps and Desert Mounted Corps won the Battle of Beersheba . Two Ottoman armies were defeated a few weeks later at the Battle of Mughar Ridge and , early in December , Jerusalem was captured following another Ottoman defeat at the Battle of Jerusalem ( 1917 ) . About this time , Friedrich Freiherr Kress von Kressenstein was relieved of his duties as the Eighth Army ' s commander , replaced by Djevad Pasha , and a few months later the commander of the Ottoman Army in Palestine , Erich von Falkenhayn , was replaced by Otto Liman von Sanders . Early in 1918 , the front line was extended into the Jordan Valley , which continued to be occupied , following the First Transjordan and the Second Transjordan attack by British Empire forces in March and April 1918 , into the summer . During March , most of the Egyptian Expeditionary Force ' s British infantry and Yeomanry cavalry were sent to fight on the Western Front as a consequence of the Spring Offensive . They were replaced by Indian Army units . During several months of reorganisation and training during the summer , a number of attacks were carried out on sections of the Ottoman front line . These pushed the front line north to more advantageous positions 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 Battle of Megiddo 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 Eighth Army ( Ottoman Empire ) at Tulkarm , the continuous trench lines at Tabsor , Arara and the Seventh Army ( Ottoman Empire ) headquarters at Nablus . The Desert Mounted Corps rode through the break in the front line created by the infantry and , during virtually continuous operations by Australian Light Horse , British mounted Yeomanry , Indian Lancers and New Zealand Mounted Rifle brigades in the Jezreel Valley , they captured Nazareth , Afulah and Beisan , Jenin , along with Haifa on the Mediterranean coast and Daraa east of the Jordan River on the Hejaz railway . Samakh and Tiberias on the Sea of Galilee , were captured on the way northwards to Damascus . Meanwhile , Chaytor ' s Force of Australian light horse , New Zealand mounted rifles , Indian , British West Indies and Jewish infantry captured the crossings of the Jordan River , Es Salt , Amman and at Ziza most of the Fourth Army ( Ottoman Empire ) . The Armistice of Mudros , signed at the end of October ended hostilities with the Ottoman Empire when fighting was continuing north of Aleppo . Entry of the United States . At the outbreak of the war , the United States pursued a policy of non - intervention , avoiding conflict while trying to broker a peace . When a German U - boat sank the British liner RMS " Lusitania " on 7 May 1915 with 128 Americans among the dead , President Woodrow Wilson 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 . The former president Theodore Roosevelt denounced German acts as " piracy " . Wilson was narrowly reelected in 1916 as his supporters emphasized " he kept us out of war " . In January 1917 , Germany resumed unrestricted submarine warfare , realizing it would mean American entry . The German Foreign Minister , in the Zimmermann Telegram , 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 . Britain intercepted the message and presented it to the US embassy in Britain . From there it made its way to President Wilson who released the Zimmerman note to the public , and Americans saw it as " casus belli " — a cause for war . Wilson called on antiwar 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 U . S . had to have a voice in the peace conference . After the sinking of seven U . S . merchant ships by submarines and the publication of the Zimmerman telegram , Wilson called for war on Germany , which the U . S . Congress declared on 6 April 1917 . 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 Selective Service Act , it drafted 2 . 8 million men , and , by summer 1918 , was sending 10 , 000 fresh soldiers to France every day . In 1917 , the U . S . Congress gave U . S . citizenship to Puerto Ricans when they were drafted to participate in World War I , as part of the Jones Act . Germany had miscalculated , believing it would be many more months before American soldiers would arrive and that their arrival could be stopped by U - boats . The United States Navy sent a battleship group to Scapa Flow to join with the British Grand Fleet , destroyer s to Queenstown , Ireland , and submarine s to help guard convoys . Several regiments of U . S . Marines 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 John J . Pershing , American Expeditionary Forces ( AEF ) commander , refused to break up American units to be used as reinforcements for British Empire and French units . As an exception , he did allow African - American combat regiments to be used in French divisions . The Harlem Hellfighters fought as part of the French 16th Division , earning a unit Croix de Guerre for their actions at Château - Thierry , Belleau Wood , and Sechault . AEF doctrine called for the use of frontal assaults , which had long since been discarded by British Empire and French commanders because of the large loss of life . German Spring Offensive of 1918 . German General Erich Ludendorff drew up plans ( codenamed Operation Michael ) 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 U . S . forces arrived . The operation commenced on 21 March 1918 , with an attack on British forces near Amiens . German forces achieved an unprecedented advance of . British and French trenches were penetrated using novel infiltration tactics , also named " Hutier " tactics , after General Oskar von Hutier . Previously , attacks had been characterised by long artillery bombardments and massed assaults . However , in the Spring Offensive of 1918 , 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 . German success relied greatly on the element of surprise . The front moved to within of Paris . Three heavy Krupp railway gun 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 national holiday . Many Germans thought victory was near . After heavy fighting , however , the offensive was halted . Lacking tanks or motorised artillery , the Germans were unable to consolidate their gains . This situation was not helped by the supply lines now being stretched as a result of their rapid advance over devastated ground . General Foch 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 Doullens Conference on 5 November 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 coordinating rather than a directing role , and the British , French , and U . S . commands operated largely independently . Following Operation Michael , Germany launched Operation Georgette against the northern English Channel ports . The Allies halted the drive after limited territorial gains by Germany . The German Army to the south then conducted Operations Blücher and Yorck , pushing broadly towards Paris . Operation Marne was launched on 15 July , attempting to encircle Reims and beginning the Second Battle of the Marne . The resulting counterattack , starting the Hundred Days Offensive , marked the first successful Allied offensive of the war . By 20 July , the Germans were back across the Marne at their starting lines , having achieved little . Following this last phase of the war in the West , the German Army never regained the initiative . German casualties between March and April 1918 were 270 , 000 , including many highly trained storm troopers . Meanwhile , Germany was falling apart at home . Anti - war marches became frequent and morale in the army fell . Industrial output was 53 % of 1913 levels . New states under war zone . In the late spring of 1918 , three new states were formed in the South Caucasus : the First Republic of Armenia , the Azerbaijan Democratic Republic , and the Democratic Republic of Georgia , which declared their independence from the Russian Empire . Two other minor entities were established , the Centrocaspian Dictatorship and South West Caucasian Republic ( 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 Transcaucasian Federative Republic was created in the spring of 1918 , but this collapsed in May , when the Georgians asked and received protection 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 . Allied victory : summer 1918 onwards . Hundred Days Offensive . The Allied counteroffensive , known as the Hundred Days Offensive , began on 8 August 1918 , with the Battle of Amiens . The battle involved over 400 tanks and 120 , 000 British , Dominion , and French troops , and by the end of its first day a gap long had been created in the German lines . The defenders displayed a marked collapse in morale , causing Erich Ludendorff to refer to this day as the " Black Day of the German army " . After an advance as far as , 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 their 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 . British and Dominion forces launched the next phase of the campaign with the Battle of Albert 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 pressure along a 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 Oberste Heeresleitung ( OHL ) issued orders to withdraw back into the Hindenburg Line in the south . This ceded without a fight the salient seized the previous April . According to Ludendorff " We had to admit the necessity . . . to withdraw the entire front from the Scarpe to the Vesle . " September saw the Allied advance to the Hindenburg Line in the north and centre . The Germans continued to fight strong rear - guard actions and launching numerous counterattacks on lost positions , but only a few succeeded , and then only temporarily . Contested towns , villages , heights , and trenches in the screening positions and outposts of the Hindenburg Line continued to fall to the Allies , 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 of St . Quentin . The Germans were now completely back in the Hindenburg Line . In nearly four weeks of fighting beginning 8 August , over 100 , 000 German prisoners were taken , 75 , 000 by the BEF and the rest by the French . As of " The Black Day of the German Army " , the German High Command realised that the war was lost and made attempts to reach a satisfactory end . The day after that battle , 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 Spa , 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 only continue the war 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 . " 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 , and on 24 September OHL informed the leaders in Berlin that armistice talks were inevitable . The final assault on the Hindenburg Line began with the Meuse - Argonne Offensive , launched by French and American troops on 26 September . The following week , cooperating French and American units broke through in Champagne at the Battle of Blanc Mont Ridge , forcing the Germans off the commanding heights , and closing towards the Belgian frontier . On 8 October the line was pierced again by British and Dominion troops at the Battle of Cambrai . 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 . Meanwhile , 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 . Knowing the government of Prince Maximilian of Baden would veto any such action , Ludendorff decided not to inform him . Nonetheless , word of the impending assault reached sailors at Kiel . Many , refusing to be part of a naval offensive , which they believed to be suicidal , rebelled and were arrested . Ludendorff took the blame ; the Kaiser dismissed him on 26 October . 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 U . S . troops kept arriving at the rate of 10 , 000 per day . The Americans supplied more than 80 % of Allied oil during the war , meaning no such loss of supplies could affect the Allied effort . Having suffered over 6 million casualties , Germany moved towards peace . Prince Maximilian of Baden took charge of a new government as Chancellor of Germany to negotiate with the Allies . Telegraphic negotiations with President Wilson began immediately , in the vain hope that he would offer better terms than the British and French . Instead , Wilson demanded the abdication of the Kaiser . There was no resistance when the Social Democrat Philipp Scheidemann on 9 November declared Germany to be a republic . Imperial Germany was dead ; a new Germany had been born : the Weimar Republic . Armistices and capitulations . The collapse of the Central Powers came swiftly . Bulgaria was the first to sign an armistice , on 29 September 1918 at Saloniki . On 30 October , the Ottoman Empire capitulated at Moudros , 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 3 November , Austria - Hungary sent a flag of truce to ask for an armistice . 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 Padua , on 3 November . Austria and Hungary signed separate armistices following the overthrow of the Habsburg Monarchy . Following the outbreak of the German Revolution of 1918 – 1919 , a republic was proclaimed on 9 November . The Kaiser fled to the Netherlands . On 11 November , at 5 : 00 am , an armistice with Germany 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 . Canadian Private George Lawrence Price was shot by a German sniper at 10 : 57 and died at 10 : 58 . American Henry Gunther was killed 60 seconds before the armistice came into force while charging astonished German troops who were aware the Armistice was nearly upon them . The last British soldier to die was Pte George Edwin Ellison . The occupation of the Rhineland 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 almost 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 stab - in - the - back legend , which attributed Germany ' s defeat not to its inability to continue fighting ( even though up to a million soldiers were suffering from the 1918 flu pandemic 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 . Aftermath . No other war had changed the map of Europe so dramatically . Four empires disappeared : the German , Austro - Hungarian , Ottoman , and Russian . Numerous nations regained their former independence , and new ones created . Four dynasties , together with their ancillary aristocracies , all fell after the war : the Hohenzollerns , the Habsburgs , the Romanov s , and the Ottomans . 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 Treaty of Versailles with Germany on 28 June 1919 . However , the American public opposed ratification of the treaty , mainly because of the League of Nations the treaty created ; the United States did not formally end its involvement in the war until the Knox – Porter Resolution was signed in 1921 . After the Treaty of Versailles , treaties with Austria , Hungary , Bulgaria , and the Ottoman Empire were signed . However , the negotiation of the latter treaty with the Ottoman Empire was followed by strife ( the Turkish War of Independence ) , and a final peace treaty between the Allied Powers and the country that would shortly become the Republic of Turkey was not signed until 24 July 1923 , at Lausanne . Some war memorial 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 to their home countries ; 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 divested Constantinople on 23 August 1923 . Peace treaties and national boundaries . After the war , the Paris Peace Conference imposed a series of peace treaties on the Central Powers officially ending the war . The 1919 Treaty of Versailles dealt with Germany , and building on Wilson ' s 14th point , brought into being the League of Nations on 28 June 1919 . Germany was forced , despite its vehement protests , to admit guilt for starting the war back in 1914 , and therefore being liable for huge reparations . Specifically Germany 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 the aggression of Germany and her allies " . Similar clauses were included into the treaties signed by the other members of the Central Powers . This clause later became known , to Germans , as the War Guilt clause ; the great majority of Germans felt humiliated and resentful on this point , and it became a major campaign issue for the Nazis in the 1920s . Overall the Germans felt they had been very unjustly dealt by what they called the " diktat of Versailles . " Schulze says , the Treaty placed Germany , " under legal sanctions , deprived of military power , economically ruined , and politically humiliated . " Meanwhile nations liberated from German rule viewed the Treaty as recognition of wrongs committed against small nations by much larger aggressive neighbors . The Peace Conference required all the defeated powers to pay reparations for all the damage done to civilians , but in practice this meant only Germany . Austria - Hungary was partitioned into several successor states , including Austria , Hungary , Czechoslovakia , and Yugoslavia , largely but not entirely along ethnic lines . Transylvania was shifted from Hungary to Greater Romania . The details were contained in the Treaty of Saint - Germain and the Treaty of Trianon . As a result of the Treaty of Trianon , 3 . 3 million Hungarians came under foreign rule . Although the Hungarians made up 54 % of the population of the pre - war Kingdom of Hungary , 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 Estonia , Finland , Latvia , Lithuania , and Poland were carved from it . Bessarabia was re - attached to Greater Romania , as it had been a Romanian territory for more than a thousand years . The Ottoman Empire disintegrated , and much of its non - Anatolian territory was awarded to various Allied powers as protectorates . The Turkish core was reorganised as the Republic of Turkey . The Ottoman Empire was to be partitioned by the Treaty of Sèvres of 1920 . This treaty was never ratified by the Sultan and was rejected by the Turkish republican movement , leading to the Turkish Independence War and , ultimately , to the 1923 Treaty of Lausanne . National identities . Poland reemerged as an independent country , after more than a century . 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 Kingdom of Serbs , Croats and Slovenes , later renamed Yugoslavia . Czechoslovakia , combining the Kingdom of Bohemia with parts of the Kingdom of Hungary , became a new nation . Russia became the Soviet Union and lost Finland , Estonia , Lithuania , and Latvia , which became independent countries . The Ottoman Empire 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 British Crown . Anzac Day , commemorating the Australian and New Zealand Army Corps , 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 theirs 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 . The establishment of the modern state of Israel and the roots of the continuing Israeli – Palestinian conflict are partially found in the unstable power dynamics of the Middle East that resulted from World War I . Prior to 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 War I were quickly imposed , sometimes after only cursory consultation with the local population . In many cases , these continue to be problematic in the 21st - century struggles for national identity . While the dissolution of the Ottoman Empire at the end of World War I was pivotal in contributing to the modern political situation of the Middle East , including the Arab - Israeli conflict , the end of Ottoman rule also spawned lesser known disputes over water and other natural resources . Health and economic effects . The war had profound economic consequences . Of the 60 million European soldiers who were mobilised from 1914 to 1918 , 8 million were killed , 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 , famine had killed approximately 100 , 000 people in Lebanon . The best estimates of the death toll from the Russian famine of 1921 run from 5 million to 10 million people . By 1922 , there were between 4 . 5 million and 7 million homeless children in Russia as a result of nearly a decade of devastation from World War I , 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 Harbin had 100 , 000 Russians . Thousands more emigrated to France , England , and the United States . In Australia , the effects of the war on the economy were no less severe . The Australian prime minister , Billy Hughes , wrote to the British prime minister , Lloyd George , " 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 epidemic typhus killed 200 , 000 in Serbia . From 1918 to 1922 , Russia had about 25 million infections and 3 million deaths from epidemic typhus . Whereas before World War I Russia had about 3 . 5 million cases of malaria , its people suffered more than 13 million cases in 1923 . In addition , a major influenza epidemic spread around the world . Overall , the 1918 flu pandemic killed at least 50 million people . Lobbying by Chaim Weizmann and fear that American Jews would encourage the USA to support Germany culminated in the British government ' s Balfour Declaration of 1917 , endorsing creation of a Jewish homeland in Palestine . A total of more than 1 , 172 , 000 Jewish soldiers served in the Allied and Central Power forces in World War I , including 275 , 000 in Austria - Hungary and 450 , 000 in Czarist Russia . The social disruption and widespread violence of the Russian Revolution of 1917 and the ensuing Russian Civil War sparked more than 2 , 000 pogroms in the former Russian Empire , mostly in the Ukraine . An estimated 60 , 000 – 200 , 000 civilian Jews were killed in the atrocities . In the aftermath of World War I , Greece fought against Turkish nationalists led by Mustafa Kemal , a war which resulted in a massive population exchange between the two countries under the Treaty of Lausanne . According to various sources , several hundred thousand Pontic Greeks died during this period . Technology . Ground warfare . World War I began as a clash of 20th - century technology and 19th - century tactics , 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 , wireless communication , armoured cars , tank 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 , indirect fire 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 field telephone . Counter - battery missions became commonplace , also , and sound detection was used to locate enemy batteries . Germany was far ahead of the Allies in utilising heavy indirect fire . The German Army employed and howitzer s in 1914 , when typical French and British guns were only and . 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 and guns and , even at the beginning of the war , had inventories of various calibers of " Minenwerfer " , which were ideally suited for trench warfare . Much of the combat involved trench warfare , in which hundreds often died for each yard gained . Many of the deadliest battles in history occurred during World War I . Such battles include Ypres , the Marne , Cambrai , the Somme , Verdun , and Gallipoli . The Germans employed the Haber process of nitrogen fixation 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 fragmentation forced the combatant nations to develop the modern steel helmet , led by the French , who introduced the Adrian helmet in 1915 . It was quickly followed by the Brodie helmet , worn by British Imperial and US troops , and in 1916 by the distinctive German " Stahlhelm " , a design , with improvements , still in use today . The widespread use of chemical warfare was a distinguishing feature of the conflict . Gases used included chlorine , mustard gas and phosgene . Few war casualties were caused by gas , as effective countermeasures to gas attacks were quickly created , such as gas mask s . The use of chemical warfare and small - scale strategic bombing were both outlawed by the 1907 Hague Conventions , and both proved to be of limited effectiveness , though they captured the public imagination . The most powerful land - based weapons were railway gun s weighing hundreds of tons apiece . These were nicknamed Big Berthas , even though the namesake was not a railway gun . Germany developed the Paris Gun , able to bombard Paris from over , though shells were relatively light at 94 kilograms ( 210 lb ) . While the Allies also had railway guns , German models severely out - ranged and out - classed them . Trenches , machine guns , air reconnaissance , barbed wire , and modern artillery with fragmentation shells helped bring the battle lines of World War I to a stalemate . The British and the French sought a solution with the creation of the tank and mechanised warfare . The British first tanks 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 combined arms teams captured 8 , 000 enemy soldiers and 100 guns . Meanwhile , the French introduced the first tanks with a rotating turret , the Renault FT , which became a decisive tool of the victory . The conflict also saw the introduction of Light automatic weapons and submachine gun s , such as the Lewis Gun , the Browning automatic rifle , and the Bergmann MP18 . Another new weapon , the flamethrower , 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 . It was a dangerous weapon to wield , as its heavy weight made operators vulnerable targets . Trench railways 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 . Naval . Germany deployed U - boat s ( submarine s ) after the war began . Alternating between restricted and unrestricted submarine warfare in the Atlantic , the Kaiserliche Marine 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 ) , hydrophone s ( passive sonar , 1917 ) , blimps , hunter - killer submarine s ( HMS " R - 1 " , 1917 ) , forward - throwing anti - submarine weapon 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 interwar period until World War II revived the need . Aviation . Fixed - wing aircraft were first used militarily by the Italians in Libya on 23 October 1911 during the Italo - Turkish War for reconnaissance , soon followed by the dropping of grenades and aerial photography the next year . By 1914 , their military utility was obvious . They were initially used for reconnaissance and ground attack . To shoot down enemy planes , anti - aircraft guns and fighter aircraft were developed . Strategic bomber s were created , principally by the Germans and British , though the former used Zeppelin s as well . Towards the end of the conflict , aircraft carrier s were used for the first time , with launching Sopwith Camels in a raid to destroy the Zeppelin hangars at Tondern in 1918 . Manned observation balloon 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 parachute 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 even 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 . War crimes . Genocide and ethnic cleansing . The ethnic cleansing of the Ottoman Empire ' s Armenian population , including mass deportations and executions , during the final years of the Ottoman Empire is considered genocide . The Ottomans saw the entire Armenian population as an enemy that had chosen to side with Russia at the beginning of the war . In early 1915 , a number of Armenians joined the Russian forces , and the Ottoman government used this as a pretext to issue the Tehcir Law ( Law on Deportation ) . This authorized the deportation of Armenians from the Empire ' s eastern provinces to Syria between 1915 and 1917 . The exact number of deaths is unknown : while Balakian gives a range of 250 , 000 to 1 . 5 million for the deaths of Armenians , the International Association of Genocide Scholars estimates over 1 million . The government of Turkey has consistently rejected charges of genocide , arguing that those who died were victims of inter - ethnic fighting , famine , or disease during World War I . Other ethnic groups were similarly attacked by the Ottoman Empire during this period , including Assyrians and Greeks , and some scholars consider those events to be part of the same policy of extermination . Russian Empire . Many pogroms accompanied the Russian Revolution of 1917 and the ensuing Russian Civil War . 60 , 000 – 200 , 000 civilian Jews were killed in the atrocities throughout the former Russian Empire . " 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 " franc - tireurs " ( guerrillas ) 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 Louvain — 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 dramatizing the " Rape of Belgium " attracted much attention in the United States , while Berlin said it was legal 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 conscripted into service . Surviving veterans , returning home , often found that they could only discuss their experiences amongst themselves . Grouping together , they formed " veterans ' associations " or " Legions " . Prisoners of war . About eight million men surrendered and were held in POW camps during the war . All nations pledged to follow the Hague Conventions on fair treatment of prisoners of war . POWs ' rate of survival was generally much higher than that of their peers 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 battle of Galicia 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 , at the Battle of Tannenberg 92 , 000 Russians surrendered . When the besieged garrison of Kaunas surrendered in 1915 , some 20 , 000 Russians became prisoners , at the battle near Przasnysz ( February – March 1915 ) 14 , 000 Germans surrendered to Russians , 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 . - 3 . 5 million men as prisoners . In some research it is stated that the number of Russian prisoners was 2 , 417 , 000 ) . 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 prior to 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 War II ) , thanks in part to the efforts of the International Red Cross 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 ( in some researches it is stated that 2 . 5 % of 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 very bad condition when captured , Ottoman officers forced them to march 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 Taurus Mountains . In Russia , when the prisoners from the Czech Legion 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 forced labor , e . g . , in France until 1920 . They were released only after many approaches by the Red Cross to the Allied Supreme Council . 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 " embedded " positions within the opposing land and naval forces . These military attaché s and other observers prepared voluminous first - hand accounts of the war and analytical papers . For example , former US Army Captain Granville Fortescue followed the developments of the Gallipoli Campaign from an embedded perspective within the ranks of the Turkish defenders ; and his report was passed through Turkish censors before being printed in London and New York . However , this observer ' s role was abandoned when the U . S . entered the war , as Fortescue immediately re - enlisted , sustaining wounds at Montfaucon - d ' Argonne in the Meuse - Argonne Offensive , September 1918 . In - depth observer narratives of the war and more narrowly focused professional journal articles were written soon after the war ; and these post - war reports conclusively illustrated the battlefield destructiveness of this conflict . This was not the first time the tactics of entrenched positions for infantry defended with machine guns and artillery became vitally important . The Russo - Japanese War had been closely observed by military attachés , war correspondents and other observers ; but , from a 21st - century perspective , it is now apparent that a range of tactical lessons were disregarded or not used in the preparations for war in Europe and throughout the Great War . Support and opposition to the war . Support . In the Balkans , Yugoslav nationalists such as the leader Ante Trumbić in the Balkans strongly supported the war , desiring the freedom of Yugoslavs from Austria - Hungary and other foreign powers and the creation of an independent Yugoslavia . The Yugoslav Committee was formed in Paris on 30 April 1915 but shortly moved its office to London ; Trumbić led the Committee . In April 1918 , the Rome Congress of Oppressed Nationalities met , including Czechoslovak , Italian , Polish , Transylvanian , and Yugoslav representatives who urged the Allies to support national self - determination for the peoples residing within Austria - Hungary . In the Middle East , Arab nationalism soared in Ottoman territories in response to the rise of Turkish nationalism during the war , with Arab nationalist leaders advocating the creation of a pan - Arab state . In 1916 , the Arab Revolt began in Ottoman - controlled territories of the Middle East in an effort to achieve independence . 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 class conflict held by radical socialists such as Marxists and syndicalists being overborne by their patriotic support for 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 . Italian nationalism 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 Gabriele d ' Annunzio , who promoted Italian irredentism and helped sway the Italian public to support intervention in the war . The Italian Liberal Party , under the leadership of Paolo Boselli , promoted intervention in the war on the side of the Allies and utilised 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 Benito Mussolini and Leonida Bissolati . However , the Italian Socialist Party decided to oppose the war after anti - militarist protestors were killed , resulting in a general strike called Red Week . 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 " Il Popolo d ' Italia " and the " Fasci Riviluzionario d ' Azione Internazionalista " ( " Revolutionary Fasci for International Action " ) in October 1914 that later developed into the " Fasci di Combattimento " in 1919 , the origin of fascism . Mussolini ' s nationalism enabled him to raise funds from Ansaldo ( an armaments firm ) and other companies to create " Il Popolo d ' Italia " to convince socialists and revolutionaries to support the war . Opposition . The trade union and socialist movements had long voiced their opposition to a war , which they argued would only mean that workers would kill other workers in the interest of capitalism . Once war was declared , however , many socialists and trade unions backed their governments . Among the exceptions were the Bolsheviks , the Socialist Party of America , and the Italian Socialist Party , and individuals such as Karl Liebknecht , Rosa Luxemburg , and their followers in Germany . There were also small anti - war groups in Britain and France . Benedict XV , elected to the papacy less than three months into World War I , made the war and its consequences the main focus of his early pontificate . In stark contrast to his predecessor , five days after his election he spoke of his determination to do what he could to bring peace . His first encyclical , Ad Beatissimi Apostolorum , given 1 November 1914 , was concerned with this subject . Seen as being biased in favour of the other and resented for weakening national morale , 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 seven - point Peace Note of August 1917 was roundly ignored by all parties except Austria - Hungary . In Britain , in 1914 , the Public Schools Officers ' Training Corps annual camp was held at Tidworth Pennings , near Salisbury Plain . Head of the British Army Lord Kitchener was to review the cadet s , but the imminence of the war prevented him . General Horace Smith - Dorrien was sent instead . He surprised the two - or - three thousand cadets by declaring ( in the words of Donald Christopher Smith , a Bermudian 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 - Dorien ' s career , or prevent him from doing his duty in World War I to the best of his abilities . Many countries jailed those who spoke out against the conflict . These included Eugene Debs in the United States and Bertrand Russell in Britain . In the U . S . , the Espionage Act of 1917 and Sedition Act of 1918 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 Irish nationalists 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 Easter Rising of 1916 , with Germany sending 20 , 000 rifles to Ireland in order to stir unrest in Britain . The UK government placed Ireland under martial law in response to the Easter Rising , although , once the immediate threat of revolution had dissipated , the authorities did try to make concessions to nationalist feeling . Other opposition came from conscientious objector 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 Stephen Henry Hobhouse , refused both military and alternative service . Many suffered years of prison , including solitary confinement and bread and water diets . Even after the war , in Britain many job advertisements were marked " No conscientious objectors need apply " . The Central Asian Revolt 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 . In Milan , 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 anarchists , 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 , Russian soldiers in France 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 October Revolution of 1917 , with the call going up for " bread , land , and peace " . The Bolsheviks agreed to a peace treaty with Germany , the peace of Brest - Litovsk , despite its harsh conditions . In northern Germany , the end of October 1918 , saw the beginning of the German Revolution of 1918 – 1919 . Units of the German Navy refused to set sail for a last , large - scale operation in a war which they saw as good as lost ; this initiated the uprising . The sailors ' revolt which then ensued in the naval ports of Wilhelmshaven and Kiel spread across the whole country within days and led to the proclamation of a republic on 9 November 1918 and shortly thereafter to the abdication of Kaiser Wilhelm II . Conscription . The Conscription Crisis of 1917 in Canada erupted when the Conservative Prime Minister , Robert Borden , brought in compulsory military service through the Military Service Act over the objection of French - speaking Quebecers . It opened a political gap between French Canadian s , who believed their true loyalty should be to Canada and not to the British Empire , and members of the Anglophone majority , who saw the war as a duty to both Britain and Canada . Out of approximately 625 , 000 Canadians who served , about 60 , 000 were killed and another 173 , 000 wounded . In Australia , a sustained pro - conscription campaign by Billy Hughes , the Prime Minister , caused a split in the Australian Labor Party , so Hughes formed the Nationalist Party of Australia in 1917 to pursue the matter . Nevertheless , the labour movement , the Catholic Church , and Irish nationalist expatriates successfully opposed Hughes ' push , which was rejected in two plebiscites . 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 and 1 , 700 , 000 were wounded . Most deaths were to young unmarried men ; however , 160 , 000 wives lost husbands and 300 , 000 children lost fathers . Legacy . 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 . 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 Commonwealth War Graves Commission , the American Battle Monuments Commission , the German War Graves Commission , and Le Souvenir français . Many of these graveyards also have central monuments to the missing or unidentified dead , such as the Menin Gate memorial and the Thiepval Memorial to the Missing of the Somme . On 3 May 1915 , during the Second Battle of Ypres , Lieutenant Alexis Helmer was killed . At his graveside , his friend John McCrae , M . D . , of Guelph , Ontario , Canada , wrote the memorable poem " In Flanders Fields " as a salute to those who perished in the Great War . Published in " Punch " on 8 December 1915 , it is still recited today , especially on Remembrance Day and Memorial Day . Liberty Memorial in Kansas City , Missouri , is a United States memorial dedicated to all Americans who served in World War I . The site was dedicated on 1 November 1921 , when the supreme Allied commanders spoke to a crowd of more than 100 , 000 people . It was the only time in history these leaders were together in one place – Lieutenant General Baron Jacques of Belgium ; General Armando Diaz of Italy ; Marshal Ferdinand Foch of France ; General Pershing of the United States ; and Admiral D . R . Beatty of Britain . After three years of construction , the Liberty Memorial was completed and President Calvin Coolidge delivered the dedication speech to a crowd of 150 , 000 people in 1926 . Liberty Memorial is also home to The National World War I Museum , the only museum in the United States dedicated solely to World War I . The UK Government has budgeted substantial resources to the commemoration of the war during the period 2014 to 2018 . The lead body is the Imperial War Museum . Cultural memory . World War I had a lasting impact on social memory . It was seen by many in Britain as signalling the end of an era of stability stretching back to the Victorian period , and across Europe many regarded it as a watershed . Historian Samuel Hynes explained : This has become the most common perception of World War I , perpetuated by the art , cinema , poems , and stories published subsequently . Films such as " All Quiet on the Western Front " , " Paths of Glory " and " King & Country " have perpetuated the idea , while war - time films including " Camrades " , " Poppies of Flanders " , and " Shoulder Arms " indicate that the most contemporary views of the war were overall far more positive . Likewise , the art of Paul Nash , John Nash , Christopher Nevison , and Henry Tonks in Britain painted a negative view of the conflict in keeping with the growing perception , while popular war - time artists such as Muirhead Bone painted more serene and pleasant interpretations subsequently rejected as inaccurate . Several historians like John Terriane , Niall Ferguson and Gary Sheffield have challenged these interpretations as partial and polemical 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 War I . 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 " these perceptions of the war , 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 . Some people were revolted by nationalism and its results , and began to work towards a more internationalist world , supporting organisations such as the League of Nations . Pacifism became increasingly popular . Others had the opposite reaction , feeling that only strength and military might could be relied upon in a chaotic and inhumane world . Anti - modernist views were an outgrowth of the many changes taking place in society . The experiences of the war led to a collective trauma shared by many from all participating countries . The optimism of " la belle époque " was destroyed , and those who had fought in the war were referred to as the Lost Generation . For years afterwards , people mourned the dead , the missing , and the many disabled . Many soldiers returned with severe trauma , suffering from shell shock ( also called neurasthenia , a condition related to posttraumatic stress disorder ) . Many more returned home with few after - effects ; however , their silence about the war contributed to the conflict ' s growing mythological status . In Britain , mass mobilisation , large casualty rates , and the collapse of the Edwardian era made a strong impression on society . 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 , Paul Fussell , 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 Nazism and fascism 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 delegitimized the Weimar government and destabilized the system , opening it to extremes of right and left . A sense of disillusionment and cynicism became pronounced , with nihilism growing . 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 . Adolf Hitler was able to gain popularity by utilising German discontent with the still controversial Treaty of Versailles . World War II was in part a continuation of the power struggle never fully resolved by World War I . Furthermore , it was common for Germans in the 1930s to justify acts of aggression in terms of perceived injustices imposed by the victors of World War I . American historian William Rubinstein wrote that : The ' Age of Totalitarianism ' included nearly all of 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 War I , without which surely neither Communism nor Fascism would have existed except in the minds of unknown agitators and crackpots . Views in the United States . US intervention in the war , as well as the Wilson administration itself , became deeply unpopular . This was reflected in the U . S . Senate ' s rejection of the Versailles Treaty and membership in the League of Nations . In the interwar era , a consensus arose that US intervention had been a mistake , and the Congress passed laws in an attempt to preserve U . S . neutrality in any future conflict . Polls taken in 1937 and the opening months of World War II established that nearly 60 % regarded intervention in WWI as a mistake , with only 28 % opposing that view . But , in the period between the fall of France and the attack on Pearl Harbor , public opinion changed dramatically and , for the first time , a narrow plurality rejected the idea that the war had been a mistake . 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 . In order 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 war effort ; 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 ; however , any analysis of the long - term effects were clouded by the defeat of these governments . Gross domestic product ( GDP ) increased for three Allies ( Britain , Italy , and U . S . ) , 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 reached 30 to 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 on Wall Street . President Wilson was on the verge of cutting off the loans in late 1916 , but allowed a great increase in U . S . government lending to the Allies . After 1919 , the U . S . demanded repayment of these loans . The repayments were , in part , funded by German reparations , which , in turn , were supported by American loans to Germany . This circular system collapsed in 1931 and the loans were never repaid . In 1934 , Britain owed the US $ 4 . 4 billion of World War I debt . 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 voting rights for women . World War I further compounded the gender imbalance , adding to the phenomenon of surplus women . The deaths of nearly one million men during the war 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 demoblised men displaced many from the workforce , as did the closure of many of the wartime factories . Hence women who had worked during the war found themselves struggling to find jobs and those approaching working age were not offered the opportunity . In Britain , rationing was finally imposed in early 1918 , limited to meat , sugar , and fats ( butter and oleo ) , 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 . Work stoppages and strikes became frequent in 1917 – 1918 as the unions expressed grievances regarding prices , alcohol control , pay disputes , fatigue from overtime and working on Sundays , and inadequate housing . Britain turned to her colonies for help in obtaining essential war materials whose supply had become difficult from traditional sources . Geologists such as Albert Ernest Kitson were called on to find new resources of precious minerals in the African colonies . Kitson discovered important new deposits of manganese , used in munitions production , in the Gold Coast . 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 the same clause was inserted , " mutatis mutandis " " in the treaties with Austria and Hungary , neither of whom interpreted it as declaration 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 . Furthermore , 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 was other acts such helping to restore the Library of Louvain . In 1932 the payment of reparations was suspended by the international community , by which point Germany had only paid the equivalent of 20 . 598 billon 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 . David Andelman 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 London Conference in 1953 , Germany agreed to resume payment on the money borrowed . On 3 October 2010 , Germany made the final payment on these bonds .