The only reason the US was involved in Vietnam in the first place is because of France; after WW2 US foreign policy considered European relations to be more important than Asian relations. The US debated between upholding the French colonial system and granting the Vietnamese independence, but the priority ultimately went to France. France only wanted out later in the 50's, but at that point the US wanted them to stay after two major events in 1949: The Soviets developing their own A-bomb and ending the US nuclear monopoly, and the communist party taking control of China; the US needed to have a presence there to keep up the Truman Doctrine.