In November 1939, the Soviet Union staged the Shelling of Mainila and invaded Finland in what became known as the Winter War, which took a disproportionally heavy death toll on the Red Army. Only in February 1940 did the Soviet forces manage to penetrate the Mannerheim Line across the isthmus, the strength of which is often exaggerated. Finland ceded the Karelian Isthmus and Ladoga Karelia to the Soviet Union in the Peace of Moscow of 12 March. According to the protocol appended to the Moscow Peace Treaty, the fighting was ended at noon (Leningrad time) on 13 March and by 26 March the Finnish troops had been completely withdrawn. The entire Karelian population of the ceded areas of about 422 thousand people was evacuated to other parts of Finland (see Evacuation of Finnish Karelia). On 31 March most of the ceded territories were incorporated into Karelo-Finnish SSR by a decision of the Supreme Council of the Soviet Union (in the Karelian Isthmus the districts of Jääski, Kexholm and Vyborg). The districts of Kanneljärvi, Koivisto and Rautu as well as the town of Terijoki were, however, included into Leningrad Oblast.