"Six-party talks and the de-nuclearization of the Korean Peninsula" is a ridiculous pipe dream.

The NKs would rather eat grass than give up their nukes.

They do not trust Russia and China sufficiently to give them the confidence that they will be supported if attacked by the US.

And the images of the dead Hussein & Qaddafy are imbedded in Kim's brain.

A dictator without nukes is likely to be taken out by the US and Kim certainly does not wish to suffer the same fate as his fellow dictators.