The Republics of the Soviet Union or the Union Republics (, soyuznye respubliki) of the Soviet Union were ethnically based administrative units that were subordinated directly to the Government of the Soviet Union. For most of its history, the Soviet Union was a highly centralized state; the decentralization reforms during the era of Perestroika ("Restructuring") and Glasnost ("Openness") conducted by Mikhail Gorbachev led to the dissolution of the Soviet Union in 1991.