The Brezhnev Doctrine was a policy introduced by Soviet leader Leonid Brezhnev in 1968. It asserted that the Soviet Union had the right to intervene in the affairs of other socialist countries to maintain communist rule. This doctrine was a response to the Prague Spring in Czechoslovakia, where reforms threatened to liberalize the government. Under the Brezhnev Doctrine, the Soviet Union justified military interventions in countries like Afghanistan and Hungary to prevent any moves toward capitalism or democracy. This policy reinforced the idea of a unified socialist bloc, emphasizing that the security of one socialist state was tied to the security of all.