The United States Enters World War I (Essential Events)

The United States entered World War I in April 1917, after years of maintaining a policy of neutrality. The decision to join the Allies came after a series of provocations and events, including the sinking of the Lusitania by a German U-boat in 1915, the interception of the Zimmermann Telegram in which Germany proposed a military alliance with Mexico against the U.S., and unrestricted submarine warfare by Germany that threatened American shipping and lives. President Woodrow Wilson, who had been re-elected on a platform of keeping the U.S. out of the war, asked Congress for a declaration of war, stating that the world must be made safe for democracy. The U.S. entry into the war provided a significant boost to the Allied powers, both materially and psychologically, and was a turning point that helped lead to the eventual defeat of the Central Powers in November 1918.