The war began in Europe in September 1939 when Nazi Germany invaded Poland. This prompted declarations of war from France and the United Kingdom against Germany.
In 1940, Germany launched a blitzkrieg invasion of Western Europe, quickly defeating and occupying the Netherlands, Belgium, and France. The British were evacuated from Dunkirk, narrowly avoiding capture.
In 1941, Germany invaded the Soviet Union, opening up the Eastern Front. The same year, Japan attacked Pearl Harbor, bringing the United States into the war against the Axis powers.
Major battles on the Eastern Front included Stalingrad, Kursk, and the siege of Leningrad. On the Western Front, D-Day in 1944 saw the Allied invasion of Normandy, eventually leading to the liberation of Western Europe.
The war in Europe ended in May 1945 with the surrender of Nazi Germany. The United States dropped atomic bombs on Hiroshima and Nagasaki, leading to Japan's surrender in August 1945, ending the war.
In total, World War II resulted in the deaths of over 70 million people worldwide, making it the deadliest conflict in human history. The war also led to major geopolitical changes and the beginning of the Cold War between the Western Allies and the Soviet Union.