The establishment of communist rule in the USSR has reasonably been regarded as the main turning-point of twentieth-century world history. The collapse of that system of government, first in Eastern Europe and then in the USSR itself, marks a turning-point that will hardly be less significant. For more than seven decades a single party had exercised a political monopoly across a sixth of the world's land surface. It dominated the electoral system and the Soviets in whose name the revolution had originally taken place. It decided all key appointments, directed the work of government, controlled the mass media, and could draw if it wished upon the assistance of a security apparatus as well as the police and army. All of this was the party's ‘leading role’, confirmed in the Constitution that was adopted under Leonid Brezhnev's guidance in 1977. The Communist Party, as a party, exercised a broader influence through its relationship with more than 100 communist or workers' parties in other countries; and the USSR, as a state, was the centre of a political and military system that dominated the destinies of about a third of the world's population.

All of this came to an end in the late 1980s, as first of all its East European allies and then the USSR itself abandoned the various characteristics of communist rule.