 The five states formerly constituting the Soviet occupation zone also had been dissolved and replaced by fifteen districts ("Bezirke") in 1952; the United States, Britain, and France did not recognize the fifteenth district, East Berlin.East Germany began active participation in the Council for Mutual Economic Assistance (Comecon) in 1950.In 1955 Prime Minister Grotewohl was invited to Moscow and, between September 17 and 20, concluded the Treaty on Relations between the USSR and the GDR with the Soviet Union which entered into force on October 6.