The Soviet Union demanded that Estonia allow the Soviet military bases and stationed 25,000 troops on Estonian soil for the duration of the European war. On 28 September 1939, the government of Estonia accepted the ultimatum and signed the mutual assistance treaty. Paldiski was made a Soviet Naval Base and its population was expelled from the town. With its new military bases in Northern Estonia, the Soviet Union invaded Finland on 30 November 1939, starting the Winter War. During 1939–1940, most of the Baltic German population from Tallinn and the Harju County countryside fled to Germany ("Umsiedlung").