Do you realize how obtuse that is? The point is how many grunts were on the ground in Vietnam itself, not how many served around the globe during the era. Good lord man. Out of around 500,000 US troops in-country only aporx 50,000 were actually in the bush fighting. Not enough to go up against every infantryman North Vietnam could infiltrate, plus varying numbers of VC depending on the year and month. So lets start with that realization, which should have been obvious, and go from there.
As for commitment? What the hell do you think commitment means? It means the desire to do whatever it takes to win.