World War II, also called Second World War, conflict that involved virtually every part of the world during the years 1939 - 1945. The principal belligerents were the Axis powers --Germany, Italy, and Japan-- and the Allies --France, Great Britain, United States, Soviet Union, and, to a lesser extent, China. The war was in many respects a continuation, after an uneasy 20-year hiatus, of the disputes left unsettled by World War I. The 40,000,000–50,000,000 deaths incurred in World War II make it the bloodiest conflict, as well as the largest war, in history. less