Lasting six years, starting with the invasion of Poland, and ending with the atomic bombs being dropped on Hiroshima and Nagasaki. This war saw most countries taking sides, between the Allies and Axis. The main Allied countries were the US, UK, France, USSR, China, and many other smaller countries. The main Axis countries were Germany, Italy, and Japan. The conflict would affect all continents but Antarctica. 70-85 million (3%) of the world population died by the end.