The DPRK is so well dug into the mountains, it would require extensive use of nuclear weapons.

Once the US releases the first nuclear weapon, then NK has the international "excuse" to use theirs on the US. The ones that are hidden in this country already.

"Why don't they use them now?" Well, nuke fuel can be traced back to the origins. If NK wants to use nuclear weapons on washington, they need to draw the US into a war and use them on the DPRK.

Once the west hits the koreas with nukes, it's all over. WW3 goes into the final stage...mutual global exchange.