Brezhnev Doctrine

"When forces that are hostile to socialism and 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."

This effectively meant that no country was allowed to leave the Warsaw pact, and the doctrine was used to justify the invasions of Czechoslovakia in 1968 as well as the non-Warsaw pact nation of Afghanistan in 1979 (see Soviet Invasion of Afghanistan).

In 1988, the new Soviet leader Mikhail Gorbachev officially abandoned the doctrine and replaced it with the Sinatra Doctrine in which each nation was allowed to develop in their own way.