If you want to see World War 3 kick off, just watch NK try for Seoul.
We'd be into it quickly and then you KNOW the Chinese would jump into the fray.
WWIII? Damn, wish I was ten years younger and a few pounds lighter.
Actually, I was still young enough to enlist (just) until January 2002- but we never went to war. At least not in the WWII sense. If the President had called for general mobilization, I was ready to go. I'd still go, if they needed me to clerk or drive truck or run construction equipment.
Last I heard they had about 20 land based ICBMs. I don't think they would leave their silos before we hit them.
North Korean conventional forces have really deteriorated and get weaker every day; what little resources they have they're pouring into strategic weapons.
They'd have no chance of making any progress with any sort of land invasion of South Korea, and they know it. Or they would have tried it already.
The Chinese have no particular interest in any such a war happening; the overwhelming concern, from their perspective, is preventing millions of North Korean refugees from crossing their borders. They'd prefer to keep the DPRK around, of course, rather than having a unified Korea under Seoul's control, but they'd rather have that than the refugee problem.
Interestingly the ROK government really doesn't want a unified Korea and doesn't want to have to pay to rebuild the North, either.