World War II, lasting from 1939 to 1945, was a catastrophic global conflict involving the Allied Powers (USA, USSR, Britain, France) against the Axis Powers (Germany, Japan, Italy). Key causes included political instability, economic devastation, and the rise of fascism, particularly under leaders like Adolf Hitler. Major events included the invasion of multiple countries, the attack on Pearl Harbor, significant battles, and the eventual use of atomic bombs, resulting in over 60 million deaths and the emergence of the US and USSR as superpowers.