A few notes:
1) An army marches on its stomach. NK is proven to be unable to feed its population in peacetime. Expect things to get worse in wartime.
NK gives priority to the army in food rationing. It is essentially a feudal state in this regard. In lots of regards actually, but I digress.
2) Tanks don't work as well in jungle. Ask the Israelis how their push into lebanon went in 06. This is important as the Merhav 4 is a more modern and respected tank than the decade-old Abrams.
Explain this to me because I am not the most military literate in this regard but:
A: Jungles did not stop tanks last time?
B: How many tanks/infantry do we have on the Korean peninsula right now? A war with NK starts with a massive artillery bombardment at...everything basically. I'm doubting many of the bases would survive. Sea lift capacity is a US strength, but it would take time for reinforcements to arrive.
3) Fixed defenses eventually fall. Ask the french in WWII.
No one builds them expecting them to survive. They're meant to be a sponge for the opponent's military strength. Both the US and the USSR built mountain fortresses during the Cold War. They were meant to suck up ICBMs and thus reduce how many could be used on other targets, not invincible fortresses.
The border is mined to all hell for a reason.
4) A side effect of endless COINops, Canadian doctrine for urban fighting has evolved into something to which destroys the garrison advantage of defending forces. I would suspect the american's doctrine to be on par at the bare minimum, if not supreme as they have had more hands on through two nations, as opposed to the hottest province of one.
NK would not be able to invade SK without Chinese assistance.
See B. I fail to see how they couldn't overwhelm the initial defense forces. I mean, Seoul is
right fucking there.
We have a bad habit in the US of assuming that the Korean War was exactly like the Vietnam War but a little earlier and somehow or another we won that one.
Most people barely know anything about the Korean War. It was actually extremely unpopular at the time and calling it a victory rather than a stalemate is a tad silly.
Any invasion of NK is always going to come down to three things:
1) Food
2) China's involvement
3) Just how effective is that state-issued brainwashing anyway?
4) US and allied forces going into a meat grinder not seen since Vietnam.
I mean I suppose that could be implied but no one's mentioned it.
Also NK has stores of chemical weapons.
No, seriously, they will have to invade SK, implode into civil war, or actually attack something before we do anything. Or have anything resembling popular/geopolitical support, for that matter.
The North Korean leadership probably values being de facto gods of their little country. So beyond sword-rattling to keep an external pressure on the populace* I doubt they'll do anything too risky.
*Iran does/did this too but the two countries aren't even remotely comparable.