The domino theory is a theory which was promoted by American foreign policy analysts during the 1950s and 1960s. According to the theory, nations on the borders of communist nations could be considered under threat, potentially falling like dominoes to communist influence and setting up a situation in which communism would rapidly spread across a region or perhaps even an entire continent. As late as the 1980s, this theory was revived to justify American intervention overseas.
Many people are familiar with the domino effect, a phenomenon which is best illustrated by thinking about a row of dominoes standing on end side by side. By making a small change to one of the dominoes in the row, the entire row will be altered as the change is magnified and passed along. The domino theory builds on this idea, viewing countries as a row of vulnerable dominoes which could collapse if one is pushed into communism.
The first mention of the domino theory occurred in a speech by Dwight D. Eisenhower in 1954. Eisenhower used this theory to explain why American intervention in Asia was crucial, because he suggested that it could lead to the spread of the “iron curtain” of communist control. The theory built on worldwide fears about communism, using the spread of the communism after the Second World War to illustrate the power of communist nations to annex and influence their neighbors.
Under the domino theory, foreign policy analysts argued, the United States had a duty to intervene overseas, to protect free nations from the scourge of communism. In addition to protecting free states, of course, this intervention would also ensure that the United States would have an entry point into regions of interest, and it could maintain profitable trade agreements with these nations.
The domino theory heavily influenced American foreign policy during the 1950s and 1960s, setting the stage for the invasion of Vietnam and justifying American activities in Korea during the Korean War. In the 1980s, the domino theory cropped up again, used by the Reagan administration to support invasion of several South American countries by American troops. Some people have also argued that it lurked in the background of the American invasion of Iraq in 2003, with the the government arguing that it needed to take action to prevent the spread of terrorism.