On November 26, the Soviet Union staged the shelling of Mainila near the border, accused Finnish troops of the provocation and requesting their withdrawal. In turn, on November 27 Finland requested a withdrawal of troops of both nations from the border area. On November 28, the Soviet Union denounced the 1932 Soviet-Finnish Non-Aggression Pact, and on November 29 broke off diplomatic relations with Finland. On November 30, 1939, forces of the USSR under the command of Kliment Voroshilov attacked Finland in what became known as the Winter War, starting with the invasion of Finnish Karelia and bombing civilian boroughs of Helsinki. On December 1, 1939, the puppet socialist government of the Finnish Democratic Republic was established under the auspices of the Soviet Union in the border town of Terijoki. On December 14 the Soviet Union was expelled from the League of Nations for waging a war of aggression. After presiding over the disastrous start of the campaign, and a disproportionally heavy death toll of Red Army soldiers, Voroshilov was replaced by Semyon Timoshenko as the commander of the front on January 7, 1940 (and four months later as People's Commissar for Defense). In mid-February, 1940, Soviet troops finally managed to break through the Mannerheim Line, and Finland sought an armistice.