[I]n the 1960s [this] was known in the West as the Brezhnev Doctrine. A month after the Prague Spring was crushed, the Soviet ideologue, Sergei Kovalev, wrote an article in Pravda which defended the use of force against progressive socialist movements willing to deviate from the Leninist-Marxist line:

“Without question, the peoples of the socialist countries and the Communist parties have and must have freedom to determine their own countries' paths of development. Any decision they make, however, must not be inimical either to socialism in their own countries or to the fundamental interests of other socialist countries.... The sovereignty of individual socialist countries cannot be set against the interests of world socialism and the world revolutionary movement. . . . Each Communist party is free to apply the basic principles of Marxism-Leninism and socialism in its own country, but it is not free to deviate from these principles.... The weakening of any of the links in the world system of socialism directly affects all the socialist countries, and they cannot look indifferently upon this.”

Brezhnev later reaffirmed these views adding that,“when internal and external forces hostile to socialism are threatening to turn a socialist country back to capitalism, this becomes a common problem and a concern of all socialist countries.” This paradigm was later used to justify Soviet troop deployments into Afghanistan in 1989.