The idea that North Korea has a significant military capability is completely false. You can go to a satellite view website and search the entire country and see that they barely have any military capability whatsoever. Their soldiers are starving. They can barely operate their equipment because of a lack of fuel. They don't have spare parts to fix their equipment and they almost certainly don't have the food stores to fight a war.
I searched the entire coastline and found 14 large submarines and 3 tiny submarines. I could not zoom in on the Mayang-Do base so they surely have a few more submarines than I saw but nothing close to the 70 or so stated by the media. Even WW2 era submarines are dangerous to ships but if the South conducted a first strike with F-35's and GPS bombs they could all be taken out in about 15 minutes.
When you look at their airbases you usually see one runway, not two or three like most US airfields. Two bombs on that one runway and one on the taxiway and their aircraft cannot take off. On satellite view you can see some aircraft lined up on their ramps, ready to go, but almost all of them are ancient Mig-19's and Mig-21's and each airfield has an aircraft junkyard. It looks like they are using those junk aircraft for parts.
The only bomber aircraft they have are a few 1960's IL-28 medium bombers that can't carry very much, maybe 6 bombs, if they are even operational. Even if they can take off with a bomb load they won't get through.
When looking at their navy bases, all of the destroyers and patrol craft are sitting in port. The smaller patrol craft are lined up side by side and the destroyers and frigates generally have their tails to the dock with a small boarding ladder off the rear. How would you reload heavy shells? Hardly any ships were at sea because they don't have the fuel to operate them. Only supply freighters were at sea. Even if these combat ships do leave port they are WW2 era ships and don't have modern aiming or over the horizon strike capability. They are no threat in a modern battle. The small rocket boats are a threat to large civilian populations but they are not a realistic military threat since their rockets are unguided.
As for the threat from their ballistic missiles, they are also a threat to civilian populations but not much of a military threat because they are probably not accurate enough. The Iraqi's launched 88 SCUD's in the first Persian Gulf War and only one hit a valuable target, a barracks.
I searched the mainland and could not find any sizeable numbers of armor. The US military says that they have everything underground but there is no way they have 7,000 tanks and armored vehicles underground. They might be camouflaged somewhere but they're not all underground. Even if they do have that many tanks and armored vehicles they are no match for the M1 Abrams tank, Apache attack helicopters, and F-35's with their infrared detectors and carrying 8 internal SDB. The Iraqi's learned that lesson the hard way.
The nuclear threat is probably no where near as realistic as some people think. Anyone can take some uranium and put it into a pile in a tunnel under a mountain and place explosives on top of it and set off a nuclear explosion but that is not a realistic weapon. It has to be small and it has to be in the right design. If it's not exactly right it will fizzle and you will just get a small explosion and a lot of radioactive material thrown out. They very likely do not have the ability to build a small nuclear bomb and have it deploy from a ballistic missile correctly.
North Korea has a large infantry force but ground troops are not going to be able to do much against armor, attack helicopters, a hundred F-16's, and stealth fighters.
If we went to war in a sneak attack it would moslty be over in 1 day. Start at midnight, submarines and destroyers launch 300 cruise missiles at military barracks, stealth bombers hit all the runways with GPS bombs, F-35's drop GPS bombs on all the destroyers and submarines, M1 tanks and Bradley's make a run to Pyongyang and Wonsan and every city in between, they will get there in 3 hours, MD-500 helicopters strafe all combat aircraft on the ground, A-10's and Apache helictopters patrol the 60 mile artillery zone, Osprey's land troops at the missile bases. If NK uses ballistic missiles with chemical or biological weapons the people just have to stay inside and any artillery that fires would be attacked by A-10's in minutes.