It was just over a year and a half ago the media - and some on this forum - were all fired up about the brilliant stroke of diplomacy behind an agreement between North Korea and the USA that would have the North Koreans freeze their nuke enrichment program and suspend nuke testing in exchange for US food aid. Two months later, NK attempted to launch a long range missile over the Sea of Japan. In Feb 2013, NK claimed to have conducted an underground nuke test. In Sept 2013,
WaPo runs an article, based on the findings of a nuke scientist at MIT, that NK is now capable to manufacturing everything it needs to support its nuke program "in house", without having to rely on any foreign-made technology, suggesting that this makes NK's nuke program effectively "sanction proof". Of course, it also puts NK in a position to be able to export its nuke program technology...to states like Iran, for example.
Yes, I know Iran is not NK. It does, however, serve to remind us that the track record of diplomacy with belligerent states isn't all that great.