You know how US is, they might try limited conventional conflict using only standing assets plus ROK and Japanese reinforments counting on Chinese and Russian nonintervention. Point of this would be not even to conquer DPRK but to tighten leash on ROK and Japan. Or maybe they completely flied off and are trying to test the defensive alliance DPRK and Russia signed few weeks ago.

I think it's more than just the US at this point though. 'western' capitalist countries are all in the same situation. UK, France, Canada... They understand the threat of BRICS to their previous economic hegemony, and there's nothing like a world war to kickstart the economy amirite

Only somewhat IMO.

The US has mobile bridge units and rebuilding corps for crossing areas and exceptional experience in doing this kind of work over the past 70 years. Let's recall for example the battle at Lake Changjin so well depicted in recent Chinese cinema. The reason that Chinese forces didn't eliminate US troops there is because the US flew a bridge or parts of it straight from Japan to the battlefront to give them an evac route after the Chinese blew up the original bridge. That's the kind of force they're dealing with. So at best it slightly slows them down. Mining does a lot more but one must consider that the US and occupied Korea may not even try to use land routes for the first few weeks of conflict. In the original Korean war turn-about for the running dogs of imperial Japan/US was achieved via massive naval landings and use of air power. Given how much coast Korea has I think that's probably part of any strategy.

In my opinion it's as much about sending a message in the vein of closing off roads, burning bridges, that kind of thing of their resolve about the south being a hostile and threatening state.