The U.S Policy of Containment is a foreign policy strategy created and executed by the US after WWII founding it's first key purpose in the Truman Doctrine of 1947. President Harry Truman warned of the evils of communism that threatened the democratic freedom of its people which like the US, the Soviet Union wanted a world made of their own virtues and expected society. The Soviet claimed they provided all citizens with economic and social rights, although, the US saw that their communism as something that controlled its citizens ways of thinking and living. It was a threat that violated both democratic rights and civil liberties of its citizens and therefore meant that America needed to make sure that it did not spread to the United States and other nations that have not yet moved politically towards Soviet Union communism. As such, this Policy of Containment stated that the US would try to stop, or contain, the spread of Communism by creating alliances or supporting the weak countries to resist Soviet advances.
I believe they used this plan in the Cold War to prevent a communism country. They tried to keep the Soviet Union from spreading Communism by providing any type of support or assistance to non-communist countries.