September 1, 1939 – September 2, 1945
Germany invades Poland, starting the deadliest conflict in human history, which ends with Japan's formal surrender on 2 September 1945.
Soviet and Mongolian forces under Georgy Zhukov defeat the Japanese on the Mongolian–Manchurian border.
Nazi Germany and the Soviet Union sign a non-aggression pact with a secret protocol dividing Eastern Europe into spheres of influence.
Britain, France, Italy and Germany agree to Germany's annexation of Czechoslovakia's Sudetenland, the high point of the appeasement of Hitler.
An organised pogrom against Jews across Germany and Austria destroys thousands of shops and synagogues, with about 30,000 people arrested.
Otto Hahn and Fritz Strassmann discover the fission of uranium nuclei; Lise Meitner and Otto Frisch explain the process shortly after.
The Royal Air Force repels a large-scale air campaign by the Luftwaffe, forcing Hitler to postpone his planned invasion of Britain.