Developed by the administration of Harry Truman in the late 1940s, the correct answer is the policy of containment.
Containment refers to the US's policy, developed by legendary diplomat George Kennan, where the US would help any free nation threatened by communism by stopping the spread of communism.
The Truman Doctrine
After World War II, Europe was in a very war-torn state, and nations were truly feeling the struggle. As the Soviet Union became more powerful, the spread of communism increased. This new idea about a government-run, equal economy appealed to nations, especially those in ruins from the war. To combat the spread of communism, President Truman introduced a policy to support war-torn countries threatened by communism in 1947. At the time, Greece and Turkey were being "threatened" by communism, and Republicans in Congress eventually won the fight to start sending assistance to Greece and Turkey. It was successful, and in 1952, Turkey and Greece joined NATO as stable, democratic nations.
The policy ultimately held strong through the decades and became the basis for containment. American Cold War policy and the idea of American military forces were never directly involved to combat this communist movement, as the idea was to give monetary assistance to nations to help them rebuild after the war, and avoid a communist revolution.
