It seems to me there would be two early warning signs of conventional open combat.
EWS1- n. korea strikes outside its territory (eg s. korea)
EWS2- usa warns foreign nationals to evacuate n. korea
EWS1 is obvious but if USA has intelligence then EWS2 could happen before EWS1.
what next?
maybe wait to see what form of combat n. korea uses and respond in roughly analogous kind, viz- conventional for conventional, and nuclear for nuclear.
if conventional i would expect the usa to use bunkerbusters on all known n. korean silos, full or empty.
if nuclear i would expect usa to bomb all coastal cities, military centers, and pyonyang.
in both cases i would expect usa to cut off all cross border movements at the PRC border with conventional means including paratroopers.
i would expect a conventional war would soon escalate to a nuclear war.
i would expect so korea to bear the brunt of the task of an invasion from the south— probably air strikes followed by paratroopers to the inner mountains, from where they could hit the fortified dmz from behind.
the n. korea subs would be hunted down and eliminated.
basically, the strategy would be quick total victory— if successful, n. korea would cease to exist as a political entity. the key would be to wait until n. korea makes the first move, which would label them as the aggressor in the eyes of world public opinion and (hopefully) make russia and PRC hesitate to come to their support.
there would have been plenty of time for usa, so korea and japan to plan something of this sort.
the stock market would tank until the invasion is complete, and then (if ww iii is avoided) recover.
I believe Donald Trump showing resolve is a lot of the financial picture we see currently. If Wall Street got nervous at the “fire and fury” talk, we couldn’t tell it.
A president with moxie and resolve is not going to be pulling punches like the Bushes and draaaaaaaaaaagging this thing out into an economy suckdown. Even having that corner of the world suffering some nuclear fallout isn’t a huge affair — and the coming rebuild of the Seoul damage AND North Korea will be a big thing. I think Wall Street might barely blink at this.