Diplomacy doesn't seem to work. Economic sanctions don't seem to work. Giving Baby Huey Kim Jong-Un a seat at the adults table doesn't seem to work. Paying him more attention than previous administrations doesn't seem to work.
In short, Jong-Un basically says..... "shove all those things up your collective asses... we will continue to manufacture and develop our nuclear capability, regardless of what anybody says."
Their people live a choreographed charade for the outside world.... the country itself is devoid of much progress, especially when compared to its southern neighbor.... but to hell with all that. Let's just plow ahead with the damn nukes.
What's it gonna take? I'd say a perfectly planned hit on Baby Huey and problem solved.