Nothing screwed us more than willingness of people to take part in conflicts.
Imagine how much harm and waste could be avoided if when generals daid, let's go liberate Afghanistan soldiers responded, nah, I'm good rather then collectively following ideas of imaginary Uncle Sam.
Did America do anything positive there? Or did they just pause natural development of that country by 20 years, to organize their little vacation from Taliban?
Rarely anything postive is achieved by going somewhere and breaking some shit and killing some folks for some time. Last few decades of USA foreign policy show it more clearly than any reasonable person should require.
I think the last few decades of USA foreign policy show that meaningful change takes time - a long time. We're still protecting South Korea, Germany, and Japan. I would consider all of those successful exercises in "nation building" as once totalitarian nations have built stable democracies.
But in Vietnam, Iraq, and Afghanistan, we simply weren't willing to stay long enough to protect the new democracies from their enemies.