Korea makes a better comparison. It took four or five years to bring the South Korean forces up to the point where they could hold the line. We were of course able to start drawing down after the Armistice. That was three years after the war started. But the lesson is that you don’t just pick up and leave and besides, we were close by in Japan.
Korea isn’t a good comparison.
While we stayed in Korea... it was because South Korea was too weak to defend itself against North Korea, a separate nation.
It was, however, strong enough to quell domestic dissent.
We’re staying in Iraq mainly because the Iraqi’s are not able to quell their internal dissent. Not because the Iraqi’s are too weak to defend against an invasion from Iran.
BTW: We never left Korea, as we are still there today. I’m posting this from the Yongsan Army Garrison in Seoul, for pete’s sake!