World War II lasted approximately six years. The war began with the Nazi invasion of Poland on Sept. 1, 1939, and ended with Japan's surrender in August 1945.
The war pitted the Axis Powers – Germany, Italy, Japan, Bulgaria, Hungary and Romania – against the Allied Powers – Great Britain, France, the Soviet Union, China, the United States and other nations. The most destructive war in history, civilian and military casualties totalled an estimated 50 million. The Allied victory sparked the creation of the United Nations, the emergence of the United States and Soviet Union as world powers and the eventual Cold War between the two.