The Continuation War, also known as the Second Soviet-Finnish War, was a conflict fought by Finland and Nazi Germany against the Soviet Union during World War II. It began with a Finnish declaration of war and invasion on 25 June 1941 and ended on 19 September 1944 with the Moscow Armistice. The Soviet Union and Finland had previously fought the Winter War from 1939 to 1940, which ended with the Soviet failure to conquer Finland and the Moscow Peace Treaty. Numerous reasons have been proposed for the Finnish decision to invade, with regaining territory lost during the Winter War regarded as the most common. Other justifications for the conflict include Finnish President Risto Ryti's vision of a Greater Finland and Commander-in-Chief Carl Gustaf Emil Mannerheim's desire to annex East Karelia.

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.