Your being a bit disproportionate there.

We left Afghanistan after holding the country for two decades. The only reason we didn't destroy the Taliban is because America sucks at fighting guerilla fighters and we gently prefer to not genocide the local population they use to hide in. But even then, after 20 years of occupation we lost less men than the terrorist attack that took us there in the first place.

I'll give it to Vietnam, they won, but you're acting like they decimated us in combat. The veitcong were barely holding on and were essentially crippled at the end of the war. Also there was a fuck ton of government incompetence during the Vietnam war. Total, "hey you know how all of our aircraft aren't built for dog fighting, a lot don't even have guns and it's best you shoot your missile when the enemy is miles out? Yeah, you can't fight the enemy until you confirm visual contact when they have the advantage. Imagine public reception if we accidentally shot down one of our own" along with, "you have one corridor you can fly your jets and planes through. No I don't care that all of North Vietnam's anti air capabilities are pointed directly at that corridor, also you're not allowed to bomb those anti air defenses because Soviet and Chinese advisors could be there" these were actual orders given to the military.

We didn't lose to the north Koreans, we had crushed them and pushed their forces up to the edge of China. We had taken almost all of the Korean peninsula. And then China literally threw millions of troops at us, pushed us back to the original border, and then even with millions of Chinese troops slamming down onto our troops and so much artillery you could not hear anything other than the drum of explosions, we still held the line. If China hadn't entered the war and started sending waves of their soldiers in a, "if we keep throwing soldiers at them, eventually they'll run out of bullets" tactic, Korea would be whole. And in the end, we managed to keep south Korea from being ruled under North Korea. Not exactly a loss. Even war wise it wasn't a loss, legally the Korean war is still on going, it's just paused.