World War II, the deadliest conflict in human history, began for Americans with the Japanese bombing of Pearl Harbor on December 7, 1941. The war was fought in two theatres, the European and the Pacific. After a key victory on D-Day, Allied troops pushed into Europe and were successful on April 30, 1945. In the Pacific theatre, the Allies were also successful after atomic bombs were dropped on the Japanese cities of Hiroshima and Nagasaki. Japan surrendered on August 14, 1945, and the treaty was signed aboard the USS Missouri. A total of 16,300,000 military personnel took part in the war, and total American casualties were 1,100,000.