Prelude to war: 1931–1938
Historians consider World War II to have begun when Germany invaded Poland on September 1, 1939. But events in the 1930s in Europe, Africa, and Asia — including several smaller wars and military actions — paved the way. (You may also want to read again about the Treaty of Versailles that ended the First World War but set the stage for the Second.)
The war begins: 1939
In 1939, German aggressions in Europe finally sparked open war.
German advances, 1940–1941
In 1940, Germany quickly occupied most of Europe and invaded the Soviet Union. Only Britain held out in the West, and the United States was gradually drawn into the conflict.