Estonia, Finland, Latvia, Lithuania, Norway, and Switzerland declare their neutrality.
The Soviet Union occupies the Baltic States on June 14–18, engineering Communist coup d’états in each of them on July 14–15, and then annexing them as Soviet Republics on August 3–6.
Germany, Italy, and Japan sign the Tripartite Pact.
The Nazis conclude that the "final solution to the Jewish problem" is extermination following relocation.
Hitler did not participate in this conference.
Wikipedia: "... an Anglo-Canadian-American document outlining the terms of coordinated development of the basic science and advanced engineering developments as related to nuclear energy; and, specifically weapons that employ nuclear energy."
Roosevelt, Churchill, Chang Kai-shek discusses allied position on Japan during the WW2, and made certain decisions regarding post-war Asia.
The Big Three agreed on a second front against Nazi Germany.
Col. Claus von Stauffenberg attempts to assassinate Hitler. Ends in failure.
Soviet Union begins the war against Finland on November 30, 1939. The war ends on March 12, 1940.
Denmark surrenders the same day, Norway resists until June.
The largest tank battle to date. Between Soviet Union and Germany. Part of the Battle of Kursk.