The Brezhnev Doctrine was a Soviet policy doctrine, introduced by Leonid Brezhnev in a speech at the Fifth Congress of the Polish United Workers' Party on November 13, 1968, which stated:
- "When forces that are hostile to socialism try to turn the development of some socialist country towards capitalism, it becomes not only a problem of the country concerned, but a common problem and concern of all socialist countries."
Implicit in this doctrine was that the leadership of the Soviet Union reserved, for itself, the right to define "socialism" and "capitalism." This meant in practice that no country was allowed to leave the Warsaw Pact or to disturb that nation's communist party's monopoly on power. The doctrine was used to justify the invasions of Czechoslovakia that terminated the Prague Spring in 1968 and of the non-Warsaw Pact nation of Afghanistan in 1979. The Brezhnev Doctrine was superseded by the facetiously named Sinatra Doctrine in 1988.