The question is a little complicated because of two American policies in effect in the immediate aftermath of WWII: decolonization and fighting communism. On the one hand, the US did not support worldwide European empires, seeing them as ultimately destabilizing. Also, many American officials saw opposing the re-establishment of European empires as the logical next step in the US policy of the Monroe Doctrine, given the pre-eminent position of the US after the war. On the other hand, the US was stunned by the "loss" of China to the communists under Mao, and Soviet attempts to expand its influence in places like Turkey and Greece. George Kennan, among others, developed a policy of containment to deal with the perceived communist threat. Thus, while the US support of France in Indochina was tepid at best, it became the ally of the South when it perceived the North move towards communism, which is why the US did not support elections to be held in Vietnam to reunite the North and South in 1954.