I'm not an expert on this topic, but tried to look up why "we haven't crushed them", i.e. why those poor, suffering people were not given the option for change

I'm not an expert on this topic, but tried to look up why "we haven't crushed them", i.e. why those poor, suffering people were not given the option for change is that it is against the interests of the USA. If North Korea were liberated then South Korea would almost automatically become an atomic power and that would create new problems. As I said, this is what I found, but there may be other reasons, like oil or who knows. What I'm certain about is that the decision is not based on a moral backbone of some sorts. But would an idealistic approach be any better?