The reason why Americans were involved in war with Vietnam war was mainly because they wanted to stop the spread of communism in Southeast Asia. The leaders from America feared that the impact of communism would gain control of Vietnam and these would have led to the fall of many nations into communism. Communism is a political and economic system that the Americans strongly opposed. Americans were sending aid to the French who were fighting in Vietnam. The Americans believed that by helping them they would prevent the spread of communist throughout the world. France was fighting those who rebelled and were led by Ho Chi Minh who was a communist and when he successfully defeated the French in 1954 that the Americans became interested and they officially became involved in trying to defeat the communists in Vietnam. Vietnam, in South East Asia was part of the old French colony known as Indo-China.
The Americans introduced the TRUMAN DOCTRINE AND CONTAINMENT policy which was stated that they were not going to allow any more countries to turn to communism and that they were going to contain the expansion of communism.
The Geneva agreement of 1954 divided Vietnam into North Vietnam and South Vietnam and Indo-Asia was divided into Laos, Cambodia, North and South Vietnam. The leader for South Vietnam Ngo Dinh Diem was a fanatical catholic and since communism hated religion he hated all that communism stood for. This is the reason why he got support from the Americans. They supported him by sending him money, supplies and military equipment. And as a result, in 1959 the communist government in North Vietnam ordered the Vietminh to begin a terror campaign against Diem’s government.