The Moscow Peace Treaty was signed, ending the Winter War between Finland and the Soviet Union.

The Moscow Peace Treaty was signed by Finland and the Soviet Union on 12 March 1940, and the ratifications were exchanged on 21 March. It marked the end of the 105-day Winter War, upon which Finland ceded border areas to the Soviet Union. The treaty was signed by Vyacheslav Molotov, Andrei Zhdanov and Aleksandr Vasilevsky for the Soviet Union, and Risto Ryti, Juho Kusti Paasikivi, Rudolf Walden and Väinö Voionmaa for Finland. The terms of the treaty were not reversed after the dissolution of the Soviet Union. The Karelian question refers to the debate within Finland over the possible reacquisition of this ceded territory.

The Winter War was a war between the Soviet Union and Finland. It began with a Soviet invasion of Finland on 30 November 1939, three months after the outbreak of World War II, and ended three and a half months later with the Moscow Peace Treaty on 13 March 1940. Despite superior military strength, especially in tanks and aircraft, the Soviet Union suffered severe losses and initially made little headway. The League of Nations deemed the attack illegal and expelled the Soviet Union from its organization.