For years events in Europe had been building toward World War I. Long term causes of the war included nationalism, imperialism, militarism, and a growing system of alliances. By June 28, 1914, Europe was like a powder keg, needing "only a spark to set the whole thing off." That spark was the assassination of the heir to the throne of Austria-Hungary. By the end of the summer Germany, Austria-Hungary, and the Ottoman Empire (the Central Powers) were at war with Great Britain, France, and Russia (the Allied Powers). The German offensive reached a stalemate along the Western Front. Here both sides dug a system of trenches from which to fight. New technology made this one of the deadliest wars in history.
When Europe went to war, most Americans believed that the events in Europe would not concern them. Although President Wilson tried to maintain U.S. neutrality, events drew the country toward war. German submarines sank U.S. merchant ships. In addition, the Zimmermann telegram increased American anger towards Germany. In April 1917 the U.S. finally declared war on Germany. American troops under the command of General John J. Pershing helped break the stalemate and turn the tide of the war. On November 11, 1918, an armistice was signed.
On the home front the war affected almost every part of American life. As industry geared up and workers marched off to fight, employment opportunities opened for women and minorities. People voluntarily rationed their use of certain food items so that the troops and Allies could be well supplied. It was also a time when government imposed stricter controls on free speech to quiet opposition to the war.
President Wilson's plan for peace—the Fourteen Points—faced opposition at the peace conference and at home. When the Treaty of Versailles was signed, the United States Senate refused to ratify it. Many senators disagreed with the proposed League of Nations. In 1921 the United States signed a separate treaty with each of the Central Powers, and it never joined the League of Nations.