Answer:
The US policy could not prevent the spread of Communism, not entirely. To the extent that governments trampled human dignity, and Communism promised a better way, then Communism was attractive to many poor people in the world.
The United States could not prevent China from becoming Communist, and failed to prevent a Communist takeover of Vietnam, to name two key examples.
Arguably, during the Cold War decades when American and Soviet foreign policies seemed based on the principle of "containing our enemy," the US had some successes ... although that remains debatable.
In Africa, Mobutu's regime was a "success" because he was never Communist. And the strongest anti-Communist nation in Africa in those years was ... South Africa.
Yes, they were as much afraid of Communists as of black people.
The Horn of Africa provides an amusing anecdote, as Siad Barre (then the dictator of Somalia) remained a Communist but refused to listen to his Russian advisers any longer because he now wanted "black Communism" and had no interest in "the white man."
The result? The Soviets turned their attention to Ethiopia and supported the Communist regime (the Derg) that had just toppled Haile Selassie. And the Americans abandoned Ethiopia (a former ally) and gave their support to Somalia, despite that nation's Communism, because Somalia hated Ethiopia and the Russians were now supporting Ethiopia.
The one success the policy had was that it helped bankrupt the Soviet Union. Not only in terms of nuclear proliferation, but also in trying to spread their sphere of influence. That led to the end, when Soviet Russia could no longer control their European satellites, and then the Soviet Union itself came to an end.
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