 The Soviet Union ostensibly sought to claim parts of Finnish territory , demanding — amongst other concessions — that Finland cede substantial border territories in exchange for land elsewhere , claiming security reasons , primarily the protection of Leningrad , which was only 32 km ( 20 mi ) from the Finnish border . ( Though the border that was " only 32 km ( 20 mi ) " from Leningrad was the end of a narrow finger of coastline about 15 km ( 9 @.@ 3 mi ) long by 5 km ( 3 @.@ 1 mi ) wide ; most of the Finnish border was more than 50 km ( 31 mi ) from Leningrad . ) Finland refused and the USSR invaded the country . Many sources conclude that the Soviet Union had intended to conquer all of Finland , and use the establishment of the puppet Finnish Communist government and the Molotov – Ribbentrop Pact 's secret protocols as proof of this , while other sources argue against the idea of a full Soviet conquest . 
