World War II (WWII or WW2), also known as the Second World War (after the recent Great War), was a global war that lasted from 1939 to 1945, though related conflicts began earlier. It involved the vast majority of the world's nations including all of the great powers eventually forming two opposing military alliances: the Allies and the Axis. It was the most widespread war in history, and directly involved more than 100 million people from over 30 countries.