World War II, fought during 1939-45, is still the greatest conflict in world history. It began with the German invasion of Poland and soon involved the other European powers. Japan and Italy allied themselves with Germany and Japan expanded through much of Asia before attacking the United States at Pearl Harbor, Hawaii in December 1941. The major land fighting was conducted in Europe, North Africa, East Asia, and the Pacific Islands, while naval fighting occurred mostly in the Pacific and Atlantic oceans. The Allied powers, led by Britain, the Soviet Union, and the United States, won in Europe in May 1945, and the U.S. bombings of Hiroshima and Nagasaki ended the Pacific war several months later.
