Why did the USA become involved in Vietnam in the 1950s and 1960s

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…actually was attacked, as some people feel that America just used it as an excuse for attacking the Vietnamese. This is only a theory, although it is as likely theory as any. In short, the USA became involved in Vietnam because they wanted to stop the domino theory. They felt that they could stop the toppling in Vietnam, and use it as a showpiece to show how capitalism could defeat communism. How wrong they were.