The idea of containment as a U.S. policy started in 1946 when George Kennan telegramed the Truman Administration explaining that the Soviets can not be dealt with as a normal government. The Soviets idea of communism is expanding throughout different parts of the world and it must be contained and therefore started the containment policy. Ultimately, the United States didn’t want the “domino effect” where more and more countries would be reeled into communism.
I think if the United States and other countries did not act out to prevent the growth of communism, most of the world would be in a communistic government. Who knows, United States may have turned into communism as well and life for everyone would be much different.