World War II was an armed conflict that began in Europe in 1939. Before its conclusion in 1945, it had spread to Asia, Africa, and small parts of North America. It claimed the lives of 15 million soldiers and around 35 million civilians, including the victims of the German program of mass murder known as the Holocaust. Ultimately, the Allied powers, including Great Britain, the United States, and the Soviet Union, defeated the Axis powers led by Germany and Japan.
Before the German invasion of Poland on September 1, 1939 finally provoked Great Britain and France to declare war on the German Reich, tensions had been mounting in Europe for two decades. The tensions were rooted in the harsh treaties of World War I, in the territorial ambitions of the European powers and Japan, as well as in Adolf Hitler's desire to establish German hegemony in Europe. From 1939 to 1941, the Axis powers succeeded in conquering most of Europe and much of Asia. However, the German invasion of the Soviet Union, and the Japanese surprise attack on the U.S. Navy at Pearl Harbor, brought the Soviet Union and the United States into the war on the Allied side in 1941. From 1942 to 1944, the Allies pushed back Axis armies in Africa, Italy, eastern Europe, and France, and regained Asian and Pacific territory they had lost to the Japanese. Following Hitler's suicide in May 1945, Germany surrendered to the Allies. Japan surrendered four months later, after the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki.
World War II made dominant global powers out of the United States and the Soviet Union, which soon became locked in a forty-year Cold War that divided Europe and Germany into two armed and mutually-hostile alliances. The war also hastened the independence of Asian and African colonies of once-dominant European countries such as Great Britain, France, and the Netherlands.
