The biggest conflict in history pitted the Allies — Britain, her empire, the Soviet Union and the United States — against the Axis powers of Germany, Fascist Italy and Imperial Japan. This bloody war, which lasted from 1939 to 1945, ripped the world apart and left millions of dead.

The immediate cause of the war was the assassination of Archduke Franz Ferdinand of Austria by a Bosnian Serb nationalist named Gavrilo Princip. The assassination triggered an international crisis that quickly grew into a worldwide conflict, with all the major European countries involved.

After the war, the world faced a period of economic instability that contributed to aggressive nationalism. Many countries practiced imperialism, which meant controlling and expanding their territory by buying or conquering other nations. This caused tension and rivalry between the conquerors, as well as dissatisfaction among colonial peoples, who were often exploited.

In 1939, a power-hungry Adolph Hitler took control of Germany. Keen to reverse the terms of the Treaty of Versailles and build his own empire, he annexed Austria and parts of Czechoslovakia. Then he invaded Poland. England and France were unable to defuse the threat through appeasement, and they declared war on Germany. In the East, Japan began to move militarily as well. Seeking influence and resources, it annexed Korea and invaded China. The United States was drawn into the war with a surprise attack on Pearl Harbor in December 1941.