The Vietnamese had to fight a long struggle first against France, and then against Japan and lastly, against USA. Following were some of the causes for the involvement of US in Vietnam: (i) First and the foremost was the fear of the spread of Communism in Vietnam. The United States (US) regarded the spread of Communism a great danger to the capitalist countries. So when Communism showed its head in Vietnam, it at once came forward to check it. (ii) US wanted to crush Vietnam at all costs to save the prestige of the capitalist countries, especially France which was an ally of the US in the Second World War. (iii) USA was against the unification of Vietnam. The Geneva Conference had divided Vietnam into two parts: North Vietnam and South Vietnam. When the Ho Chi Minh government in North Vietnam and National Liberation Front in South Vietnam tried to unify the two parts, in violation of the Geneva Conference, US could not tolerate this. Hence, it decided to intervene in Vietnam.