What were some factors which made the French Army less successful than their later American counterparts in effectively fighting the Vietnam War?
The only real factors that made the French lose more quickly than the US were A) the French were less committed to trying to hold on and B) they were less well-funded and equipped than American forces.
Tactically and strategically, the French had the same problems the US did. They had a hard time distinguishing between people who were or might be friendly and those who were Viet Minh. They struggled because of the fact that the Viet Minh were back by and could take refuge in China. They faced a hugely popular enemy in Ho Chi Minh and the Viet Minh.
France had much less in the way of resources to use to combat these problems. 80% of their war effort was being paid by the US, but France was still struggling to get back on its feet after WWII. It simply did not have the financial and industrial power to back a major war.
Secondly, France was not as committed to keeping up the fight. Opinion in France turned against the war much more quickly than opinion in America did. France did not see itself as the defender of the free world against communism.
Thus, I would argue that the French Army was less successful due to the fact that it had fewer resources and less political support than the US did.