The United States became involved in the Vietnam War primarily because it wanted to prevent communist North Vietnam from conquering South Vietnam. The spread of communism was a major concern for the United States during the Cold War era, and it viewed the conflict in Vietnam as part of its broader containment policy aimed at preventing the spread of communism in Southeast Asia and beyond. The fear was that if South Vietnam fell to communism, it could lead to a domino effect, with other countries in the region also succumbing to communist influence. Therefore, the U.S. provided military and financial support to South Vietnam in an attempt to prevent the communist forces of North Vietnam from taking over the country.