Define the domino theory and the brezhnev doctrine and discuss how they affected the foreign policies of both the united states and the soviet union during the cold war?

The domino theory is a foreign policy theory of the United States Government. 
The Brezhnev Doctrine was a Soviet foreign policy, first and most clearly outlined by S. Kovalev in a September 26, 1968 Pravda article, entitled “Sovereignty and the International Obligations of Socialist Countries.” This is the doctrine that was used to announce the justification of the Soviet invasion of Czechoslovakia. This was considered by the Soviets to be a needed defensive and strategic buffer in case there was any kind of hostilities to break out with the West. When used in practice, the policy meant that there was limited independence of communist parties that was allowed
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