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.

Finland, officially the Republic of Finland, is a Nordic country in Northern Europe. It borders Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bothnia to the west and the Gulf of Finland to the south, opposite Estonia. Finland covers an area of 338,145 square kilometres (130,559 sq mi) and has a population of 5.6 million. Helsinki is the capital and largest city. The vast majority of the population are ethnic Finns. Finnish and Swedish are the official languages, with Swedish being the native language of 5.1% of the population. Finland's climate varies from humid continental in the south to boreal in the north. The land cover is predominantly boreal forest biome, with more than 180,000 recorded lakes.