What happens if the rest of the world decides to strike first with e.g. a massive wave of conventional missiles and bombers, combined with a ton of defensive mines air-dropped into the DMZ?
Would it be enough to take out North Korea's nuclear capability and cripple troop encampments on the DMZ enough that they can't immediately launch a massive counterattack on South Korea?
I'm not an expert but according to conventional wisdom, NK has enough conventional-arms firepower (mainly artillery) to do massive damage to Seoul before they're taken out. Looking at a map, it's a bit unnerving how close Seoul is to the internal Korean border.
Does anybody have any idea why is it that way? Considering the obvious threat, why haven't they tried shifting away from there? I agree an entire city can't be moved, bu the "Capital" nature of it can be.
Rhetorical question: what's the biggest potential target in New York State? Albany, or NYC?
You could move the government, but it wouldn't matter. Seoul would still completely dominate South Korea. Their entire economy and around half their population is based in the Seoul metro area. It's only a mild exaggeration to say that Seoul is South Korea.
China would retaliate or threaten to. If, in your scenario, you imagine China would be join in with "rest of world" then your scenario is about as likely/realistic as NK saying "sorry, jk, our bad" and surrendering to US/SK (who, btw, are still at war with NK).
North Korea has a very long history of breaking it's treaty commitments and violating diplomatic agreements.
That said, all-out massive attack isn't viable. there would be no way to disguise the political and military preparations for such an attack, and China wouldn't allow it anyway. Bear in mind the the South Korean capital Seoul is within medium artillery range of the border, and there are a lot of North Korean artillery pieces aimed at it. Even without a nuclear attack capability, North Korea could do them an awful lot of damage in ways that would be difficult to prevent.
The issue, as always, is cost/benefit. N. Korea has always tried to walk the line between wanting to seem strong enough that you can't just toss the leaders out and not so threatening that you actually worry they might mess you or your allies up.
It's not worth it to the U.S. or anyone else to invade, lose 30K-100K soldiers and then have to rebuild the country, and it never has been. The nuclear arms race serves partially as a deterrent against possible invasion, and partially an attempt to get people to the negotiating table for some resources by scaring Japan and N. Korea enough that they want to deal with this.
But if they had the capability, they still don't have the desire to use it as a first strike since that would give every country around + the U.S. a reason to bomb them to the ground.
This was the main idea behind the South African nukes as well. If memory serves, the country had only 6 nuclear warheads, but they were never meant to be anything but a deterrent (and probably a display of power and capability).
That said, if Japan decided it _wanted_ nuclear weapons, it can almost certainly produce them itself very quickly (order of 6-12 months according to most estimates I've seen). They have the raw fissile material due to their longstanding nuclear power plant program, and the general knowhow and infrastructure. https://en.wikipedia.org/wiki/Japanese_nuclear_weapon_progra... has some more data.
That's the point. I don't want destabilization. But if that's your goal, you can get it pretty quickly without any need for a sneak attack by conventional forces.
A batch of kindly old grannies with popguns could cripple NK's military capability.
The problem is, they have hundreds (thousands?) of artillery pieces buried in mountain bedrock and pointed at Seoul. Even if we dropped paratroopers on Great Leader's palace and captured him in the first two hours, it is simply not possible to find, let alone knock out, all of the artillery within a few days, which is how long it would take for them to level Seoul.
...If any of them still work. An awful lot of NK's military equipment hasn't been maintained for decades and has rusted solid where it sits. So the artillery could be one big bluff, for all we know. But can we risk it, with South Korea's largest city at stake?
Would it be enough to take out North Korea's nuclear capability and cripple troop encampments on the DMZ enough that they can't immediately launch a massive counterattack on South Korea?