Dissolution of the Soviet Union
The Soviet Union was formally dissolved and ceased to exist as a sovereign state and subject of international law on 26 December 1991. It also brought an end to the Soviet Union's federal government and to Soviet leader Mikhail Gorbachev's efforts to reform the Soviet political and economic system in an attempt to stop a period of political and economic stagnation.
Source: Wikipedia — Dissolution of the Soviet Union (CC BY-SA 4.0)