Mikhail Gorbachev introduced reforms in the Soviet Union known as perestroika and glasnost. Perestroika restructured the Soviet political and economic system to transition to a market economy. Glasnost promoted openness and transparency. Gorbachev's reforms weakened the Soviet Union and led to revolutions in 1989 in Eastern Europe that overthrew communist governments. This caused the Soviet Union to abandon the Brezhnev Doctrine and lose control over Eastern Europe. It also led to the reunification of Germany.