Economic challenges in the Soviet Union caused by the inefficiency of a planned economy vs western free-market economic policies.
Internal political reforms and openness (Glastnost and Perestroika) promoted by Soviet leader Mikhail Gorbachev, which inadvertently weakened the communist system.
Economic and technological competition from western countries during the arms race, straining Soviet resources.
Deteriorating relationships between the Soviet Union and its satellite states in Eastern Europe.
Strategic arms limitation treaties (SALT) and diplomatic engagement between the United States and the Soviet Union.
Social unrest and pro-democracy movements in Eastern European countries like Poland, Hungary, and Czechoslovakia.
Reunification of Germany in 1990, facilitated negotiations to reduce nuclear weapons arsenals.
Ultimately, the combination of these factors led to the erosion of communism and Soviet control in Eastern Europe, culminating in the dissolution of the Soviet Union in 1991 and the end of the Cold War.