World War II (1939-1945) was a global conflict involving the Allied powers (primarily the United States, the United Kingdom, the Soviet Union, and France) against the Axis powers (mainly Germany, Japan, and Italy).
It began with the German invasion of Poland and extended across Europe, Asia, and Africa. The war witnessed the use of brutal tactics, the Holocaust, and massive bombings.
The United States entered the war following the Japanese attack on Pearl Harbor. The conflict concluded with the surrender of Germany and Japan after the atomic bombings of Hiroshima and Nagasaki, leaving global devastation and setting the stage for the Cold War.