I agree with you as far as saying, "yeah, it shouldn't have be just us, but a coalition of nations." But as with Iraq, it seems like every time that happens the US winds up being the main player anyway, out of sheer competence if nothing else.
It seems to me that when issues like this become apparent-- Afghanistan, Iraq, Iran, Korea, etc-- most nations (including the US) are sensible enough to agree that something should be done, but the burden of responsibility somehow always ends up in the lap of the United States, simply due to unwillingness on everyone else's part to make the necessary investments (which, I do agree, the US maybe has also overestimated its ability to handle). Even when European nations join in coalitions, they don't stay around long enough to do any real fighting or to help rebuild. Still, it always seem odd to me, ( that is, the general European sentiment of, "do nothing now, bitch about your country's relative unimportance in national affairs later"). I'm not saying that's definitely how it really works, but that's at least the impression I get.
That said, while I don't think the North Korea government would be as easy to eliminate as Iraq's, I also think rebuilding would be quite a bit easier. But then again I'm not really sure just how brainwashed the North Korean people are. I've heard good theories that if the US ever went to war with China or North Korea, there'd be somewhat of a chance that their armies would actually turn on the government.