January 1, 1940
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
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
Operation Weserübung — 1940 code name for Germany's assault on Denmark and Norway during the Second World War
1940 Winter Olympics — edition of the Winter Olympics, scheduled in Sapporo, Japan, canceled due to World War II
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
1940s — decade of the Gregorian calendar (1940–1949)
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