Answer: CONTAINMENT
Futher details/context:
There was also an idea known as "domino theory" that was applied in justifying US involvement in the Vietnam War. Domino theory said that the spread of communism in Vietnam would result in other countries in the region falling like dominoes to the influence of communism.
Domino theory was a corollary to the policy of containment that developed as the United States' policy regarding communism after the end of World War II. George F. Kennan is known for recommending the policy of containment. Kennan was an American diplomat in Moscow after World War II. In 1946, he sent what became known as "the long telegram" of his advice about what the USA needed to do about the Union of Soviet Socialist Republics (USSR). In those days, everyone feared an ultimate confrontation between the USA and the USSR -- that the Cold War would someday explode into a massive heated conflict between the superpowers. Kennan, in Moscow, had much foresight to see the internal problems the USSR had. He advised not pushing the conflict too much, but instead just try to "contain" the Soviet Union and wait for their system to collapse under the weight of its own problems. Kennan was right. It took almost 50 years, but eventually the communist system in the USSR fell apart. [The Union of Soviet Socialist Republics came to an end in 1991.]
