Selling a war to the US population requires a moral justification. A National Interest argument won't do because that would be called "neo-imperialism" and get the anti-colonialists all riled up. This prevents the formulation of clear goals for military actions. Believing your own BS is never a good idea. Our adversaries can pursue their clear interests, which gives them an advantage.
Then there's the "Pottery Barn" principle, where you go into the pottery barn, smash all the pottery, clean it up, and "make it better" after chasing off the proprietor to a comfortable retirement in Dubai. However, if you have a good reason to smash up the Barn, you can leave it that way. After 9-11, smacking the Taliban made sense but sticking around to build schools was a form of self-flagellation. Let Pakistan and India arm their Afghan proxies after leaving -- that'll be punishment enough.
The Iraq war was a mistake based on faulty intelligence or outright lies, your choice.
