The collapse of the Soviet Union was caused by a combination of long-term stagnation and short-term reforms.

The centrally planned Soviet economy had been stagnating for decades, unable to compete with the West or provide adequate consumer goods.

The immense cost of the nuclear arms race and the long, unwinnable war in Afghanistan crippled the Soviet economy.

Mikhail Gorbachev became the Soviet leader in 1985 and introduced a series of major reforms.

His policy of 'glasnost' (openness) allowed for greater freedom of speech and criticism of the government.

His policy of 'perestroika' (restructuring) was an attempt to reform the stagnant economy.

These reforms, intended to save the system, instead unleashed forces that destroyed it, such as nationalism and widespread public discontent.

In 1989, a series of largely peaceful revolutions overthrew the communist regimes in the Soviet satellite states of Eastern Europe.

The fall of the Berlin Wall in November 1989 was the most powerful symbol of this collapse.

The Soviet Union itself formally dissolved into 15 independent republics in December 1991, officially ending the Cold War.