American Victims of the Lusitania, photograph by George Grantham Bain, May 1915
Ten months after World War I began in Europe, a German submarine torpedoed the British ocean liner RMS Lusitania off the southern coast of Ireland without warning. Within 20 minutes, the vessel sank. More than 120 Americans were among the nearly 1,200 casualties. The attack, followed by others on American vessels, increased support among members of Congress and the public for entering the war.
Prints and Photographs Division, Library of Congress
World War I: Declaring War on Germany
On April 2, 1917, President Woodrow Wilson asked a joint session of Congress to declare war on Germany. The president cited Germany’s repeated submarine attacks on passenger and merchant ships and its attempt to entice Mexico into an alliance against the United States as his reasons for Congress to declare war. On April 4, 1917, the Senate voted in support of the measure, and the House concurred two days later. The United States later declared war on German ally Austria-Hungary on December 7, 1917.
We are going to war . . . to vindicate our honor and to maintain our independence as a great nation. We are going to war . . . in defense of humanity.
Senator Gilbert Hitchcock of Nebraska, Speech to the U.S. Senate, April 4, 1917