North Korea: What Exactly Is The Problem?

According to various recent news reports, U.S. Secretary of State John Kerry dismissed as "unacceptable by any standard" weeks of dire warnings of impending nuclear war by North Korea and said Washington would never accept the reclusive state becoming a nuclear power.

But the core issue at hand is not whether or not North Korea will be "accepted" as a nuclear-powered nation, but rather...what exactly is it that they want?  What is the issue?  What is it that is forcing its leader to be so aggressive and divisive?

What is the problem, and how can THAT issue be resolved – with diplomacy, the highest good for all those concerned – and without bloodshed or global annihilation?