True about Vietnam. Applying WW II logistic scales, you could have conquered that country in a few weeks (and have an ugly partisan war at your hands for decades). Trouble is neither China nor Russia would have allowed that mass of US military presence in their backyard (just like you wouldn't have with them in South America as your backyard). So you settled for playing with your military superiority (and the lessons learned in Vietnam have now made the US Army the best equipped infantry in the world). You fought just enough so that the North Vietnamese could not win and thought that would eventually wear them out - it didn't, they were fighting for a cause, like it or not, and proved persistent (in any case an Asian trait and then the Vietnamese are regarded as "the Prussians of Asia" to boot). They wore you out (psychologically, not logistically of course) and South Vietnam was a weak and corrupt puppet state, unable to give its war against the North any significance.
You should have sided with the North. Uncle Ho was an admirer of the American Constitution and of Abraham Lincoln (no doubt, he saw South Vietnam as the Confederacy). If there is one red (no pun intended!) thread of ineptitude running through US foreign policy it is your abysmal choice of allies in the Third World. You mostly manage to end up on the side of regimes beyond their zenith and then stay by their side until their death throes scratching your head at what went wrong. And if you support a liberation movement by accident then they end up blowing up your WTC a few decades later. Some fine friends!
