World War I

(1914–18) International conflict between the Central Powers—Germany, Austria-Hungary, and Turkey—and the Allied Powers—mainly France, Britain, Russia, Italy, Japan, and (from 1917) the U.S. After a Serbian nationalist assassinated Archduke Francis Ferdinand of Austria in June 1914, a chain of threats and mobilizations resulted in a general war between the antagonists by mid-August. Prepared to fight a war on two fronts, based on the Schlieffen Plan, Germany first swept through neutral Belgium and invaded France. After the First Battle of the Marne (1914), the Allied defensive lines were stabilized in France, and a war of attrition began. Fought from lines of trenches and supported by modern artillery and machine guns, infantry assaults gained little ground and were enormously costly in human life, especially at the Battles of Verdun and the Somme (1916). On the Eastern Front, Russian forces initially drove deep into East Prussia and German Poland (1914) but were stopped by German and Austrian forces at the Battle of Tannenberg and forced back into Russia (1915). After several offensives, the Russian army failed to break through the German defensive lines. Russia's poor performance and enormous losses caused widespread domestic discontent that led to the Russian Revolution of 1917.

Other fronts in the war included the Dardanelles Campaign, in which British and Dominion forces were unsuccessful against Turkey; the Caucasus and Iran (Persia), where Russia fought Turkey; Mesopotamia and Egypt, where British forces fought the Turks; and northern Italy, where Italian and Austrian troops fought the costly Battles of the Isonzo. At sea, the German and British fleets fought the inconclusive Battle of Jutland, and Germany's use of the submarine against neutral shipping eventually brought the U.S. into the war in 1917. Though Russia's armistice with Germany in December 1917 released German troops to fight on the Western Front, the Allies were reinforced by U.S. troops in early 1918. Germany's unsuccessful offensive in the Second Battle of the Marne was countered by the Allies' steady advance, which recovered most of France and Belgium by October 1918 and led to the November Armistice. Total casualties were estimated at 10 million dead, 21 million wounded, and 7.7 million missing or imprisoned. &Seealso; Battles of Caporetto and Ypres; Fourteen Points; Lusitania; Paris Peace Conference; Treaties of Brest-Litovsk, Neuilly, Saint-Germain, Sèvres, Trianon, and Versailles; Edmund H.H. Allenby, Ferdinand Foch, John French, Douglas Haig, Paul von Hindenburg, Joseph-Jacques-Césaire Joffre, Erich Ludendorff, John Pershing.