The correct answer is "if one country became Communist, others would follow".
The Domino Theory was developed in 1950 and proposed the idea that is a country came under the influence of communism, its neighbors will probably follow suit. A consequence that would be known as "the Domino Effect". In order to neutralize this, The United Stated created numerous alliances and collaboration treaties with many regimes around the world in order to prevent the advance of Communism.
