The Republics of the Union of Soviet Socialist Republics or the Union Republics () were national-based administrative units of the Union of Soviet Socialist Republics (USSR). The Soviet Union was formed in 1922 by a treaty between the Soviet republics of Byelorussia, Russia, Transcaucasia, and Ukraine, by which they became its constituent republics. For most of its history, the USSR was a highly centralized state despite its nominal structure as a federation of republics; the decentralization reforms during the era of perestroika and glasnost conducted by Mikhail Gorbachev are cited as one of the factors which led to the dissolution of the USSR in 1991 and the creation of the Commonwealth of Independent States. There were two very distinct types of republics in the Soviet Union: the larger union republics, representing the main ethnic groups of the Union and with the constitutional right to secede from it, and the smaller autonomous republics, located within the union republics and representing ethnic minorities. The Karelo-Finnish Soviet Socialist Republic, a relic of the Soviet-Finnish War, became the only union republic to be deprived of its status in 1956. The decision to downgrade Karelia to an autonomous republic within the RSFSR was made unilaterally by the central government without consulting its population. Overview The chapter 8 of the 1977 Soviet Constitution is titled as the "Soviet Union is a union state". The article 70 stated that the union was founded on principles "socialist federalism" as a result of free self-determination of nation and volunteer association of equal in rights soviet socialist republics. The article 71 listed all of 15 union republics that united into the Soviet Union. According to Article 76 of the 1977 Soviet Constitution, a Union Republic was a sovereign Soviet socialist state that had united with other Soviet Republics in the USSR. Article 78 of the Constitution stated that the territory of the union republic cannot be changed without its agreement. Article 81 of the Constitution stated that "the sovereign rights of Union Republics shall be safeguarded by the USSR". In the final decades of its existence, the Soviet Union officially consisted of fifteen Soviet Socialist Republics (SSRs). All of them, with the exception of the Russian Federation (until 1990), had their own local party chapters of the All-Union Communist Party. Outside the territory of the Russian Federation, the republics were constituted mostly in lands that had formerly belonged to the