The Paris Peace Conference convened in January 1919 and did not officially close until one year later, after Germany formally ratified the Treaty of Versailles, but Wilson, Lloyd George, and the leading foreign dignitaries left for home in late June, as soon as the Germans signed their treaty. The Allies designated ambassadors or under-secretaries to represent them in the conclusion of the treaties for Austria (St. Germain), Bulgaria (Neuilly), Hungary (Trianon), and the Ottoman Empire (Sèvres), the latter two not signed until 1920. As the US secretary of state, Lansing, had feared, Wilson’s direct involvement at the conference reduced him to the level of just another negotiator and his Fourteen Points to mere bargaining chips, most of which were sacrificed in whole or in part to achieve the fourteenth: the creation of the League of Nations. While the provisions regarding Germany (reparations, war guilt, near-disarmament, and loss of territory and colonies) received the most attention, outcomes haunting the world into a second great war (and in some cases, beyond it) included the borders drawn in the dismemberment of Austria-Hungary and the Ottoman Empire, as well as the decision of the conference to disregard the interests of Russia and, to a lesser extent, Italy.

The entry of the United States doomed the Central Powers in the long run but not during 1917, as the collapse of Russia deprived the Allies of their largest army at a time when the Americans could not yet make good the loss. Unable to afford a repeat of the bloody battles of 1916, the Germans resolved to stand on the defensive in the west while the U-boats (and the Bolsheviks) did their work. Meanwhile, the failure of Nivelle’s spring offensive nearly broke the French army, leaving it paralyzed by mutiny for much of the rest of the year, while British and Imperial troops attacked at Arras and Vimy Ridge in the spring, then at Passchendaele in the summer and autumn, gaining little ground at great cost. A November attack at Cambrai, ultimately indecisive, showed how tanks could be used effectively. On other fronts, Russia’s attempt to use Czech deserters against Austria-Hungary was more successful than Germany’s efforts to use Polish deserters against Russia, but not decisively so. The Allies added Greece to their ranks by overthrowing its pro-German king, but nearly lost Italy after the Central Powers achieved a decisive victory at Caporetto, and lost Romania when Russia sued for peace.

The European war quickly escalated into a world war, owing to the global nature of European colonial empires, commercial interests, and naval presence. The entry of Japan, honoring its alliance with Britain, caused the fighting to spread to East Asia and the Pacific islands. Admiral Graf Spee’s squadron abandoned Germany’s Chinese base at Tsingtao (which Japan took in November 1914), then steamed eastward across the Pacific to the coast of Chile, where Spee defeated a British squadron off Coronel in November before being crushed by another British squadron off the Falklands in December. While Japanese, Australian, and New Zealand troops occupied Germany’s Pacific island colonies, British, French, and Belgian forces attacked Germany’s four African colonies. Three of them fell quickly, but in German East Africa (the future Tanzania), troops under Lettow-Vorbeck resisted Allied forces for over four years, until the Armistice. During and after the pursuit of Spee’s squadron, Allied (mostly British) warships swept the world’s oceans of German cruisers, ending the naval war beyond European waters and the North Atlantic. This decisive success facilitated the unimpeded movement of men and supplies from around the world to bolster the Allied cause in Europe, and led Germany to embrace unrestricted submarine warfare.

“Thank God, it is the Great War!” General Viktor Dankl, commander designate of the Austro-Hungarian First Army, penned these words on July 31, 1914, the day it became clear that the dispute between Austria-Hungary and Serbia, stemming from the assassination of Archduke Francis Ferdinand a month earlier, would not be resolved peacefully or limited to a Balkan war. Forty-three years had passed since the last war that matched European powers against each other and, like many European military officers of his generation, Dankl, then fifty-nine, feared he would serve his entire career without experiencing such a conflict. On August 2, when Dankl in another diary entry referred to the rapidly escalating conflict as “the World War,” he could not have imagined just how accurate the label would become: that the action would extend to the Far East, the South Pacific, and sub-Saharan Africa, that more than a million men from the British and French empires would see action on European battlefields, that the United States would have an army of more than 2 million men in France just four years later, or that European countries would account for a minority of the states participating in the postwar peace conference.

Many of the war’s leading generals rose or fell during 1916. Germany refocused on the west, where Falkenhayn, chief of the high command since the initial defeat at the Marne, attacked at Verdun, seeking a bloodletting that would drive France from the war. The French persevered through ten months, during which generals Pétain and Nivelle eclipsed Joffre, who lost his post as commander late in the year. In the summer Haig’s British and Imperial forces, with French support, attacked the Germans at the Somme, where in September tanks first saw action. The battle there ended in a draw but also ensured the French a draw at Verdun. Meanwhile, on the Italian front, Conrad von Hötzendorf launched an Austro-Hungarian offensive from the Tyrol. This attack, like the German effort at Verdun, used troops pulled from the east, allowing a summer Russian offensive under Brusilov to break the weakened front. The Germans returned troops to seal the breach, but the debacle forced Falkenhayn to relinquish the high command to Hindenburg and Ludendorff. Amid the crisis the Central Powers made William II their supreme commander, sealing Austria-Hungary’s subordination to Germany. Bulgaria and the Ottoman Empire joined them late in the year in crushing Romania shortly after it joined the Allies.

The resumption of unrestricted submarine warfare in February 1917 caused the United States to sever relations with Germany, though President Wilson held out hope for peace until learning that the German foreign secretary, Zimmermann, sought to turn Mexico against the US and use it as an intermediary to turn Japan against the Allies. Amid these tensions Nicholas II was overthrown and succeeded by a Provisional Government, ultimately led by Kerensky, which made the fateful decision to keep Russia in the war. In April 1917, days after the United States declared war, Germany gave Lenin transportation home from Switzerland, hoping he would foment a second revolution and knock Russia out of the war. Following the Bolshevik Revolution of November 1917, Lenin indeed concluded an armistice with the Central Powers, but only after his appeal for a general peace “without annexations or indemnities” failed. The net result of the United States replacing tsarist Russia gave the Allies an ideological cohesion they had lacked previously. While Wilson characterized their war as a fight for universal rights and freedoms, the entry of the United States gave them millions of fresh troops to go with the capital, munitions, and supplies they were already receiving from American sources.

In the world of 1914 the great powers of Europe were divided into rival blocs: the Triple Alliance, in which Italy and Austria-Hungary tolerated each other for the sake of friendship with Germany, and the Triple Entente, in which France, Russia, and Britain (three countries with little in common, which more often than not had been enemies rather than friends) were drawn together by their mutual fear of Germany. Beyond Europe, the United States and Japan had emerged as great powers in their own right, Japan tied to Britain by alliance. The British Empire, with its self-governing dominions along with its colonies, remained the envy of other aspiring imperial powers. Experiences from the Anglo-Boer war (1899-1902), Russo-Japanese war (1904-5), and Balkan wars (1912-13) helped shape the strategies, tactics, arms, and equipment of the armed forces of 1914. Nationalism, Darwinism, and arms races contributed to tensions in the prewar years, during which the Balkans emerged as Europe’s most volatile region. Among the Balkan states, Serbia emerged as the most volatile but also the most ambitious. Beyond the Balkans, Europe’s smaller and weaker countries were steadfastly neutral; among them, only Belgium and Portugal became embroiled in World War I.

World War I’s legacy is most obvious in Europe, which it left with more small states dependent upon international organizations for their security. Wilson’s League of Nations – minus his own United States – failed to provide that security, leading many interwar Europeans to blame his compromised idealism for the rise of fascism and another world war. In the long run, however, Wilson’s ideals of self-determination, democracy, collective security, and an international rule of law were embodied in the European Union. Beyond Europe, the war transformed the Middle East by encouraging Zionism, Arab nationalism, and the Turkish model of secularism, along with the Islamist backlash against all three. Farther afield, it spawned communist movements that eventually took over in China and Vietnam, as well as the Indian and Pakistani nationalism that divided south Asia. For countries whose losses in World War II did not approach those of World War I – Britain, Canada, Australia, and New Zealand, along with France and Italy – the remembrance and commemoration of World War I remains a part of national life. For Germany, Russia, the United States, and Japan, World War II became the more historically significant experience, for its role in making or breaking those countries as world powers.

During the last half of the war each of the European powers experienced a serious crisis on its home front. Britain resorted to conscription and suppressed a rebellion in Ireland. In both France and Italy, morale wavered when the army suffered mutiny and defeat. In Germany, the militarization of the home front under the Hindenburg Program coincided with the struggle to feed the civilian population during the “turnip winter.” Meanwhile, the death of Francis Joseph accelerated revolutionary thinking among the nationalities of Austria-Hungary. Amid growing sentiment for peace on the European home fronts, the international socialist movement held a peace conference at Stockholm which attracted more participants than the earlier effort at Zimmerwald but was just as fruitless. In the last half of the war strong civilian leaders emerged to rally the home front in each of the leading European Allies – Lloyd George in Britain, Clemenceau in France, and Orlando in Italy – while in the United States, Wilson’s ideals lent a veneer of unity to a degree of domestic upheaval not seen since the American Civil War. Women’s contributions to the war effort bolstered the cause of women’s suffrage, with Britain granting it in March 1918, to take effect in the first postwar elections.

The war’s last year began with the Germans in negotiations with Soviet Russia that resulted, in March 1918, in the draconian Treaty of Brest-Litovsk, but only after they had countered Bolshevik stalling tactics by continuing to march eastward, to the detriment of their own plans to withdraw troops for a final offensive in the west. Nevertheless, the final German drive was strong enough to compel unprecedented Allied cooperation, including making Marshal Foch supreme commander. By July the Germans were closer to Paris than at any time since 1914, but American troops gradually assumed a greater role against them, with two-thirds of the 2.1 million to cross the Atlantic deployed to the front by the armistice. British and Imperial troops ultimately mastered combined arms warfare, using artillery, infantry, tanks, and air power to achieve a breakthrough at Amiens in August from which the Germans never recovered. On the Balkan front, a multinational Allied army achieved a breakthrough in September that knocked Bulgaria out of the war, and a month later a breakthrough on the Italian front precipitated the collapse of Austria-Hungary. In the war’s last hundred days, the Allies liberated almost all of France and half of Belgium, prompting Germany to sign the armistice on November 11.

After their failure at Gallipoli in 1915, attempts by the Allies to undermine the Ottoman Empire ranged from the eastern Sahara to the Arabian desert, with the resources of India becoming indispensable to the effort against the Turks, especially in Mesopotamia. Returning to India from South Africa in 1914, Mahatma Gandhi supported the war on the grounds that a strong showing would strengthen India’s hand in its relationship with Britain. Most Indians rallied behind the Allied cause and, thanks largely to T. E. Lawrence, Arabs sustained a successful revolt against the Turks. The British had no intention of giving India the degree of self-government that it wanted, and they and the French had no intention of rewarding the Arab contribution with postwar independence (and especially not with Palestine, which the Balfour Declaration of 1917 promised to the Zionists), but within the context of World War I the ends appeared to justify the means. Just as the wartime movements in India and the Arab world foreshadowed future developments, Turkey’s Armenian genocide presaged subsequent state-sponsored attempts to exterminate specific civilian populations. On the fringes of the war in the Middle East, local conflicts from Darfur to Ethiopia and Somalia likewise pointed the way to a grim future.