The Vietnam had just defeated the French army.
The main reason behind America's involvement in Vietnam was its fear of communism spreading. It believed that something called the Domino Theory would take place in Vietnam spreading communism into Eastern Europe. They believed this because they had seen it happen. The Soviet Union had become communist during the First World War and had spread it to China. The Americans had just been fighting a war in Korea trying to combat communist rule and now the communists in Vietnam had just defeated the French army. America believed that if it was not stopped then communism would keep spreading.
In 1954 a group called Vietminh lead by Ho Chi Minh defeated the French Army, which was occupying Vietnam at the time, Ho Chi Minh was a communist and although most people who supported it did so because it was opposing French rule not because it was communist American still believed that the Vietminh would bring communism to Vietnam and therefore had to be stopped.
This lead to Americafirst becoming involved in Vietnam because with the French defeated the future of Vietnam was uncertain so there was a peace conference in Geneva. At the Geneva Conference it was decided that Vietnam would be split in two up to the 17th parallel and elections would be held two years later and the country would be reunited again. America wasn't happy with this agreement and started supporting South Vietnam's Government lead by a man called Ngo Dinh Diem.
America got involved with the Diem Government because it believed that if they kept South Vietnam strong and anti communist then that would stop the domino theory from occurring. Unfortunately this didn't work. Diem was a vicious and cruel dictator who could never win over the support of the people like the communist had done in the North Vietnam's countryside. When hefirst came into power he put an end to the Vietminh and any members still in South Vietnam. He automatically assumed th…