1. I do not consider it likely that North Korea will have the means to successfully deliver nukes to population concentrations in S. Korea, Japan, or the US. As far as I know this is expert consensus. It has had impressive successes in both nuclear weaponry and long-range rocketry in the past year, but there is still no concrete evidence of the successful coupling of the two technologies. Without that, you are just going to get a far shorter and less intensive – and likely not that much more accurate – version of Germany’s V-2 attacks against London in 1944-45 (with just three civilian deaths/rocket, one of the least effective military investments ever).
2. The construction of a survivable deterrent capacity is a separate project that will take many more years and might in any case be beyond North Korea’s capacity anyway.
3. The actual strength of the North Korean Army might be closer to 700,000 troops (the widely cited one million figure is now suspected to be more of a fantasy). Furthermore, I don’t see a large percentage of these being credibly combat-worthy. It’s no secret that the North Korean military doubles as a source of cheap labor, from helping with the harvest to road repairs and construction. This is time that they don’t spend training. Healthcare is at a Third World level. That recent defector was swimming in parasites, and those are border guards which could be expected to be more privileged and politically reliable than average. There has since been yet another defector. This raises questions about the real state of morale in its forces.
The often quoted figure of 200,000 “special forces” I suspect are the only ones loosely equivalent in quality to regular First World armies. However, even they are much more technologically obsolete. For instance, even at the most elementary level, none of the North Korean soldiers I have seen in videos ever seem to have body armor – something that has long been standard in modern militaries. As commenter peterAUS also noted, the last experience of real military conflict that North Korea had was more than half a century ago. How much do North Korean generals, and no less importantly, officers, know about modern developments in military theory?
North Korea does indeed have some genuinely “special” special forces with impressive feats over the decades. However, by analogy with other countries, there can’t be more than a few thousand of them.
One more note on morale. Although North Koreans have never lived better – hardly a high bar to clear relative to the barracks socialism of Kim Il-Sung and the famines of Kim Jong Il – this has also translated into a large material gap between elites and commoners. To be sure, North Korea has always had draconian, legally entrenched class differences that would put any capitalist country to shame (read about Songbun), but it is only in the past decade that is has become more visible than ever before – that is, the Pyongyang elite now has cars and access to department stores, while the rest have only have bootleg DVDs about the unimaginable quality of life in China and South Korea. And we know from cliodynamics that rising inequality is the death of asabiya. Unclear if unprivileged conscripts would still want to fight for such a country.
4. North Korea’s air defense system is extremely dense, and with over 150 AAA positions, Pyongyang is the most defended city in the world. But the guns and fire-control radar are of 1950′s/60′s Soviet vintage.
Much good they will do against this scenario (which is itself from 2003):
Six B-2s each armed with 80 500-lb JDAMs sequentially launch from Guam. The strike is coordinated with several divisions of B1-s with 12 JDAMs per aircraft and F-117s with two laser-guided precision-guided weapons per aircraft, taking off from other bases in the region. These strikes would be deconflicted with the launch of more than 300 Tomahawk cruise missiles from the various cruisers and submarines positioned in the Pacific. Six additional B2s, flying out of their homebase in Missouri, time their arrival closely behind – loaded with 24 1,000lb JDAMs or 16 2,000lb JDAMs. One thousand targets could be destroyed prior to sunrise.
5. The US has by far the best SIGINT in the world, and more of it is concentrated per square kilometer in North Korea than on any other country in the world.
Recent leaks indicate that voices within the Trump administration, including McMaster and Trump himself, want to “punch North Korea in the nose,” for instance, by destroying a launch site while the North Koreans are prepping for a new missile test. They should have no problems in doing so.
I do not believe it at all likely that China will intervene. While China has a formal alliance with North Korea, which it has publicly affirmed it will keep, it has no love lost for KJU and would not mind him getting taken down a peg or two. Another thing that few people mention is that both China and Russia have good relations with South Korea, and are unlikely to want to jeopardize them for the sake of Rocket Man. Neither China nor Russia want a nuclear armed North Korea, which could potentially rebound on them; and should this provoke a pro-Chinese military coup against KJU, then all the better for Beijing.
Consequently, the smart thing for North Korea to do at that point would be to swallow their pride and leave matters be.
6. North Korea has no proportionate means to retaliate against this. Maybe it could just about manage to lob a missile at Japan or Guam, with few chances that they will hit anything important, but that will just invite a much harsher retaliation against its military infrastructure.
7. What North Korea could do unleash its massive artillery forces against Seoul – the “soft” WMD doomsday scenario on the Korean peninsula. This might add up to a few 10,000′s of deaths before they are fully suppressed, especially if chemical weapons munitions are used.
This means total war, of course.
As I wrote, “I suspect it will be a harder nut to crack than Iraq in 2003, or even 1991. It is an ultranationalist regime with a formidable secret police, so you’re [probably] not going to be buying any generals off. North Koreans have higher IQs than Iraqis (so more competent), do not practice inbreeding (so more cohesive), and a have a lot more hills, mountains, and tunnels (which partially negate South Korean/American technological predominance).”
Still, this doesn’t make up for the vast technological gap (which some “anti-imperialist” writers seem to brush off as of no consequence). A South Korean victory over the North is pretty much inevitable, with the KPA getting much the worse of the exchange and ceasing to exist as a coherent force within a couple of weeks if not a few days.
Perhaps the regime’s best technologically feasible bet to stall and massive increase costs for the advancing South Koreans and Americans would be to use nuclear mines (an idea touted by NATO in the 1950s to counter Soviet numerical superiority). Not much the advancing forces will be able to do about this, and will increase their military deaths from 1,000′s or even 100′s, into the 10,000′s.
If China is smart (and they are) they would use the opportunity to try to foment a pro-Chinese military coup against KJU, and/or to take direct control of most of the country under the pretext of defending it from American aggression. With North Korea existentially engaged in the south and the Chinese-North Korean border denuded, this should be a trivial task. Americans end up expending most of the political capital, South Koreans do most of the bleeding (apart from the North itself), and the Chinese end up with most of the actual territory, which it could then leverage in post-war negotiations.