Hitler's invasion of Poland in September 1939 led to the outbreak of the Second World War.
During the early stages, the conflict was confined mainly to Europe, but later extended to the rest of the world following the Japanese attack on Pearl Harbor which led to the United States also entering the war.
The "total war" mobilized the economic and industrial resources of all belligerents and caused the death of some 50 million people, most of whom were civilians.
The war ended with the fall of Berlin to the Red Army in May 1945 and the bombing of Hiroshima and Nagasaki in early August 1945.