Though the conflicts began much earlier, World War II did not officially begin until September 1, 1939. The massive war ended 6 years later in 1945.
World War II was a struggle between the Allied nations, led by Britain, and the Axis nations that were led by Nazi Germany. Over 30 countries in total participated in the war, making it one of the largest and most significant conflicts in history. Though the Allies were the victors of the war, winning was not without negative effects. One result of the war was two Allied nations, the United States and the USSR, entered into a Cold War that lasted for the rest of the century. Over 50 million lives were lost in World War 2, with the USSR losing 42,000,000 people alone.