There are many reasons.
Firstly, the US couldn’t expand the scale of the war. As for the US,it might lose if not expand the scale, but it must lose if it expanded. The biggest enemy of the US is the Soviet union, and the most important place it should protect is the Europe. If the US expand the scale of the war in Vietnam, pitting a large number of troops to the place where is far from the Europe, complaining with Chinese army but not the Soviet union. It means that the US give their weaknesses exposed to the Soviet union, and consuming it’s power in an unlikely threat to European rivals. Therefore,expand the scale of war, whether and how the dozen, the United States …show more content…
In fact, according to Lanchester guerrilla warfare model, a battle, number of regular troops need to be sent at least 8 times the guerrilla forces troops to win, and only sent 6 times in the United States, want to win chance and will pay a heavy casualties, the United States announced the idea is rational choice;
Internationally, big geopolitical support - the Soviet union and China, two top centralized power support, in dealing with the United States, to win by conventional battle is very difficult;
Geographically, Vietnam jungle and mountainous terrain, is advantageous to the north Vietnamese hidden ambush and supplies to smuggle, detrimental to the mechanical forces rapid advance, if it is exposed to plain terrain, may the north Vietnamese casualties will be more;
Tactical, north Vietnam effectively offset the American firepower advantage through combat fortifications, reduce their casualties, forcing the United States can only withdraw.
The decadent capitalist democracy of society, does not allow their President to put a lot of people's life and wealth, wasting for a long time on other countries' civil war which is rooted in