The Soviet Union adopted the "policy of combating 'anti-socialist forces'" which became known as the Brezhnev Doctrine in "reponse to the efforts, early in 1968, of the Czechoslovakian Communist Party, under the leadership of Alexander Dubcek, to introduce a number of reforms, including the abolition of censorship. The Soviet Union adopted a policy of combating 'anti-socialist forces'."
On November 14, 1968, Soviet leader Leonid Brezhnev, in a speech delivered at the Fifth Congress of the Polish United Workers' Party, "justified the August 20 invasion of Czechoslovakia, stating that 'Czechoslovakia's detachment from the socialist community would have come into conflict with its own vital interests and would have been detrimental to the other socialist states.'
"This justification would remain a policy in the future to protect communism from outside influences and secure the centralized power of Moscow over its satellites. It was known in the West as the Brezhnev Doctrine and would remain influential until 1989, when Mikhail Gorbachev denounced the policy." Read Brezhnev's speech.