The Soviet Socialist Republics were administrative entities of the USSR that existed between 1922 and 1991. During the Brezhnev period, there were fifteen federated republics subordinate to the Moscow-based government. These republics were formed in the early 1920s on the basis of ethnic criteria related to the Stalinist perception of the national question. At the republican level, the fifteen entities had local political branches (except for the foreign affairs and defense) that were independent in theory, but in practice implemented the decisions of the central government. There were three republics in Transcaucasia and five in Central Asia.