The domino theory motivated democratic nations to fight against communism. It was believed that nations, especially in Asia due to it's proximity to large communist forces such as China and the USSR, would fall to communist control one after the other like dominoes. This spurred the US to partake in aid for the republic of Korea.
Due to the American fear of the domino theory, means of communism finding its way to American society, America began to aid South Vietnam. South Vietnam was an advocate of Anti-Communism, which attracted US citizens. Anything against communists, in American eyes, was worth aiding in any form.
April 7, 1954 – Dwight D. Eisenhower gives his "domino theory" speech during a news conference. The domino theory was a theory prominent from the 1950s to the 1980s, that speculated that if one country in a region came under the influence of communism, then the surrounding countries would follow in a domino effect. The domino theory was used by successive United States administrations during the Cold War to justify the need for American intervention around the world.