World War I (1914–18) was already under way when, in May 1915, a German U-boat (submarine) sank the British passenger ship, the SS Lusitania in the North Atlantic Ocean off the coast of Ireland. Launched in 1907 by the British Cunard Line, the ship was the largest passenger ship afloat. When the Lusitania was downed, 1,200 civilians, including 128 Americans, were killed. U.S. President Woodrow Wilson (1856–1924) warned Germany that another such incident would force the United States to enter the war. Germany heeded the warning for a time, but later began attacking American cargo ships, forcing the United States to enter the war on the side of the Allies (Serbia, France, Great Britain, Russia, and nineteen other nations).
Further Information: "Lusitania." MSN Encarta. [Online] Available http://encarta.msn.com/index/conciseindex/OF/00FDD000.htm, October 25, 2000; Martin, Gilbert. The First World War: A Complete History. New York: Henry Holt, 1994; "(Thomas) Woodrow Wilson." MSN Encarta. [Online] Available http://encarta.msn.com/index/consiseindex/16/concise/.asp?mod=1&ti=0166B000&page=6, October 25, 2000.