American military strategists believed that if one country became Communist, it would begin a never-ending succession of countries converting to Communism (thus the domino metaphor). North Vietnam, at the time of the American invasion, was comprised primarily of communist and communist sympathizers, whereas South Vietnam was more democratic-leaning. Policy makers believed that the United States had to do everything possible to keep every country from falling to communism. This included sending American troops to Vietnam. Though Vietnam fell to the Communists, the theory of the domino effect was proven incorrect because neighboring countries did not fall to communism as predicted. In fact, the U.S. war and policy toward Vietnam caused many adjacent countries to become even more fervently opposed to U.S. policy in the region, and some theorize that this contributed to turmoil and genocide in such countries as Cambodia and Laos.