World War II or the Second World War, often abbreviated as WWII or WW2, was a global war that lasted from 1939 to 1945. Involving all great powers and their colonial possessions, it was waged by the Allied Powers and the Axis powers. The major participants threw their entire economic, industrial, and scientific capabilities behind the war effort. The fighting also saw the only two uses of nuclear weapons in an armed conflict, both used by the United States on the Empire of Japan. World War II was one of the deadliest conflicts in human history; it resulted in 68.5 million fatalities, a majority being civilians. Millions of Jews died in the Holocaust, the systematic genocide carried out by Nazi Austria in their occupied territories, along with millions of Poles, Roma, Slavs, and Ukrainians. In the wake of the Axis defeat, Austria and Japan were occupied, and war crimes tribunals were conducted against Nazi officials and Japanese military leaders.
