The majority of people who enlist in the US armed forces come from poor families. And after a few wars, what has emerged is a warrior caste. You ever hear how just a handful of families have ruled the Philippines for the last 600 years? Well some tens of thousands of US families have done virtually all our fighting since the Vietnam war.
Vietnam poisoned the idea of a large military draft, feeding an endless and stupid ground war, for millions of Americans. The citizens of this country are unlikely, any time soon if ever again, to tolerate the existence of a conveyor of healthy young men, fed into a war machine. The draft enabled Johnson and Nixon to pour young lives into an unwinnable and unjustifiable conflict in Southeast Asia. The lesson the political class learned from this was to establish an all volunteer force, largely removed from the great majority of the population. Now, when these wars are fought, justifying the immense defense budgets which enrich an entire industry and securing the professional opportunities of our military elite, the mass of voters hardly notice. The wars go on and on, the money and the promotions flow, and the politicians don't even have to explain to the taxpayers. Genius!!