A green screen with the text 'DOMINO THEORY' at the top. Below it, there is a paragraph of text that reads: 'The belief that one country's fall to communism will lead to a chain reaction of other countries falling to communism. This theory was popularized by the United States during the Cold War. The belief was that if one country in Southeast Asia, such as Vietnam, fell to communism, it would lead to a domino effect and other countries in the region would also fall to communism. The real of the region would soon follow. The United States believed that it was necessary to prevent this domino effect by intervening