This all depends on victory conditions. The U.S. "won" Korea, Iraq, Vietnam, and Afghanistan in the same sense that they "won" WW2 - those countries were bombed back into the stone age and the existing governments fell. But WW2 was fought as the U.S. was an ascendant (but not dominant) power among a number of peer rivals, and the U.S. was not the aggressor. It felt like a victory, because we emerged as the dominant power, with the only industrial base that wasn't destroyed, and then enjoyed the economic fruits of rebuilding a country that had been bombed back into the stone age and then capitulated. Additionally, Germany and Japan expected that U.S. occupation would be absolutely terrible, that we would be tyrants in the same way that their militaristic governments of the time were, and so when it turned out we just wanted to make money, that was a huge relief to them.

With all the post-WW2 wars, we've gone in as a dominant power, as the aggressor, to a country that is far smaller and less developed. In terms of casualties, they've been even more lopsided victories than WW2. The second Iraq war killed about half a million Iraqis and displaced about 1.8M, vs. < 1000 Americans killed, for a kill ratio of ~500:1. But what does it even mean to achieve victory here? We go in as a bully and ruin our world reputation. The average American sees zero benefit from killing Iraqis; it just means higher oil prices, larger government debt, more inflation, reduced civil liberties, and a lack of focus on domestic problems (...which may be the point). Defense contractors make out like a bandit, and the executive branch gets to consolidate power (...which, again, may be the point), but there isn't room to grow the way there was after WW2.