N. Korea has had hundreds of artillery pieces aimed at the Demilitarized Zone (that is to say, aimed at U.S. troops) for decades, as leverage. They have nukes, even bigger leverage.
These two factors alone make it unthinkable for U.S. planners to decide to steamroll N. Korea. For the past few decades, NATO/U.N./Pentagon victims have been (mostly) defenseless third world countries which have been covertly destabilized in advance to make it even easier to wreck their society.
Obviously, I'm not in favor of it. Carpet bombing, steam rolling, whatever you call it, is atrocious, costly in many ways, and usually extremely cost-ineffective.
It's not the fixed arty targeting troops that's the fear. I mean, I'd rather not have stuff coming down at my tank on a balistic arc like that, but I can move fast enough to deal with it.
From my view, the two Koreas are teetering between reconcilation and irrevocable hostility. Tending towards a frigid state right now.
One guy in Korea pinpointed the positions of many hundreds of artillery pieces and their effective range from Google Maps satellite images; it was impressive, the effort. Seoul can become a sea of fire easily if it comes to that.
It's this.
If you'd like a scenario where a steamroller is going to occur, then this is what'll happen (at least in my humble opinion): tensions will start to escalate to all hell and back again, to the point where the ROK armies and the US start reinforcing the DMZ to a much greater extent then now. This is to say, that instead of a fortified border, there's a couple of brigades of heavy armor sitting there getting ready to rock (I'll send pictures, or more likely not, but preeeeetty good odds that I end up there in this scenario). Eventually, it's possible that the risk of NK opening up with all their fixed becomes great enough to force our hand, at which point we'll see the single greatest preemptive (or near-preemptive. Some chance that we're hopeful enough not to move, or they decide to be preemptive) action in history as we do our damnedest to stop all those tubes from firing. I don't think that we'll be successful.
However, we'll smash them to little pieces (probably at fair cost to ourselves, not even including all the damage that they can inflict to civilian South Korea). The disparity between the three armies is just far too great for anything else to happen. I mean, it's not the cold war anymore, but that doesn't mean we've lost absolute dominance in set piece battles. Now, how fucked up the occupation would be, that's another question. Especially when you consider the logistic problems of trying to reintegrate a country like North Korea back into the world. I'm pretty sure that China won't be terribly happy with the number of refugees they'd have a result.
Has anything changed? If Americans land on NK, NK activates nuclear bomb = no more American landing. Steamrolling is still not an option.
Ummmm no? North Korea doesn't have the capability to stop a determined invasion. I mean, yeah, assuming that they can produce and deliver a warhead, they might be able to kill a lot of American pr South Korean forces, but they don't have 1965 Crocketish capability to close down the DMZ by turning it into an irradiated wasteland.
North Korea has a gun pointed at the South with all the fixed emplacements. However, we've got one pointed at them that'll kill them, while theirs will just serious mess us up.