World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world’s countries—including all of the great powers—eventually formed two opposing military alliances: the Allies and the Axis. It was the most global war in history; it directly involved more than 100 million people from over 30 countries. In a state of total war, the major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities.