It's different really, we struggle when we're put against guerrilla warfare and people who are civilians one minute, then pick up an AK47 and snipe at you the next. Put us up against an organised army and we steam roll. If you want to cite the Iraq war, go on Wikipedia and look at the losses for each side, we lost 172 soldiers in the Invasion of 2003 compared to estimates of 7,000-45,000. That's nothing but an overwhelming victory.
It's even easier when the military just put down their arms and dissolve into the civilian population. Which is what happened in Iraq V2. We didn't steam roll them, most didn't even fight, which is the point. It's doubtful NK would do the same. They probably would actually fight.
Vietnam was 50 years ago and didn't start off as an all out conventional war on the part of the US but rather assistance to the southern Vietnamese govt that escalated and turned into a more conventional war in places and a drawn out counter insurgency campaign.
If we look at recent wars then we can indeed look at Iraq - twice! Saddam had one of the largest militaries in the region and was overwhelmed very rapidly. These days there isn't a single country that could stand up to the US for very long in a conventional war. Sure a counter insurgency is a different scenario however it isn't clear that that would be too much of an issue here (China dependent to some extent). It isn't like we're dealing with any Islamic nonsense there and China's current implementation of 'communism' is rather far removed from North Korea.
Frankly if something did kick off down there then we're looking at a large conventional war which would require decisive US action very quickly.
See above (edit; and also Rroffs post), and include the fact that Iraq was a desert, which is flat and allows large armoured columns with huge ranges of visibility. A big negative for conventional forces with lower tech weapons and a big benefit for well equipped militaries with top of the range tanks, armoured vehicles and planes. Add lots of trees, hills, narrow passes into the mix and things change almost immediately, as was found out in both Korea and Vietnam. It nullifies a lot of the advantages of western militaries as you need to start putting a lot more men on the ground, not protected by thick steel shells. The US had huge firepower in Vietnam for example (heck they were using B52's to carpet bomb huge areas).
NK would "degenerate" into Vietnam style fighting very quickly IMO, and the idea we would just steamroll through as easily as somewhere like Iraq (during the first few weeks) is wishful thinking at best. The US would win, but at huge political and manpower costs and I don't believe there would be the political will required to do so, just like vietnam.
