Isn't this pretty much 99.9% of the reason nobody has yet done anything about NK, and will continue to do nothing about NK. Even with all the posturing and weapons testing.The biggest issue is how quickly the US could destroy the forces which could damage Japan and South Korea. There is no debate that country against country Korea will come last, probably within 24 hours of anything kicking off, but a few shells or missiles hitting down town Tokyo or suchlike would be a real mess and that is a real fear in the current state. Nuclear would not be used by US first I do not believe but should Korea launch one then I fear the US would destroy most of the major population areas in 10 minutes. US has always had a policy of you hit us with a nuke, we hit you with 1000 and I think this would happen, they have history of like big bombs after all.
If the North decide on a scorched earth policy and their military has the stomach to execute that order, SK at least would be devastated.
Being theoretically able to hit the US with a nuke really isn't the main threat. It's what they could do to their neighbours.
But this also means that NK really doesn't have a strong hand either, surely. The only reason they aren't being "liberated" is because nobody wants SK to be damaged. But if NK invaded the South then there is little reason for the West to hold back any longer. So in that event NK essentially gives up the hunan shield keeping the West at bay, no?
Even where they are now NK still doesn't have a winning hand. They don't have a serious nuclear deterrent and they need SK as it is to prevent the West from invading.
Sort of catch 22.