During World War II from 1941 to 1945, 16,112,566 served, 405,400 were killed, and 671,846 were wounded. The United States joined the Allies, Britain, France, Russia, and China, to fight the Axis Powers, Germany, Italy, and Japan, after the U.S. military was attacked by the Japanese at Pearl Harbor in 1941. U.S. military forces saw action in Asia, the Pacific, Europe, and North Africa. This was the largest and most expensive war ever. Germany surrendered in May 1945, and Japan surrendered in September 1945 after atomic bombs were dropped on Japan to avoid the additional loss of life that an invasion of the four main islands of Japan would have caused. The political instability caused by the war forced the United States to end its isolationist policy and take an active role in the world during peacetime.