1940 Summer Olympics — Games of the XII Olympiad, firstly scheduled in Tokyo, Japan, rescheduled in Helsinki, Finland, finally canceled due to World War II

The Holocaust in Poland — genocide of Jews in Nazi-occupied Poland during World War II

Second and final stage of the 1947–1949 Palestine war

1947–1948 Civil War in Mandatory Palestine — civil war between the Jewish and Arab communities of Palestine which is the first phase of the 1948 Palestine War

Katyn massacre — Soviet mass murder of ca. 22,000 Poles in several parts of European Russia, including in the Katyn forest, which became a pars pro toto name for the whole massacre

Operation Weserübung — 1940 code name for Germany's assault on Denmark and Norway during the Second World War

1940s — decade of the Gregorian calendar (1940–1949)

Battle of Britain — air battle waged between German and British air forces in 1940

First war of the Arab–Israeli conflict

Bombing of Tokyo — 1940s air raids by the United States Air Force in WWII

German AB-Aktion in Poland — 1940 military operation