Final answer:
The Brezhnev Doctrine was a policy that justified Soviet intervention in Eastern Europe to protect socialist rule, reflecting the Soviet Union's concerns for security and stability in its sphere of influence.
Step-by-step explanation:
Soviet leader Leonid Brezhnev put forth the Brezhnev Doctrine, which stated that any threat to socialist rule in Central and Eastern Europe would require intervention by fellow socialist states. This doctrine justified the Soviet intervention in Eastern Europe, most notably the crushing of democratic movements, under the premise that it was necessary to protect the overall interests of socialist nations within the Soviet sphere of influence. It was, in many ways, a response to the perceived threats to the stability and security of the Soviet Union and its allied socialist states.