Ideological justifications for the Vietnam war?

Vietnam was the second "hot" battle of the cold war (korea was the first). Had not the "Cold War" been in effect, the US MAY not have had very much justification for it's involvement. The US also operated "anti-communist" missions in Central/South America (e.g. Che Guevara). But, Vietnam was closer to the Communist Superpowers, and more easily supplied...the communist insurgency in Central/South America could NOT re-supply so easily, so they fizzled out (with US Gov't support). Without "Supplies" wars cannot be fought.