North Korea is an isolated country, poverty stricken, paranoid, apparently self-sacrificial and amazingly persistent in international confrontations, as is now being demonstrated. It is a cultural and almost sacred commitment for its leaders not to back down, even in the face of international condemnation and the most severe political and economic pressure.
... As the  crisis escalated, The Carter Center was finally given reluctant permission from President Clinton for me to visit Pyongyang. A satisfactory agreement was concluded and later confirmed by both governments, with participation by South Korea, Japan and others. But neither side honored all the commitments...
... There are other issues, but the basic North Korean demand is a firm non-aggression commitment from the United States, which U.S. officials continue to reject. The U.S. insists first on a complete end to the North Koreans' nuclear program, which they have refused to accept. If neither side will yield or compromise, then an eventual military confrontation seems likely. The United States can prevail, but with terrible human casualties in both North and South Korea.
There must be verifiable assurances that prevent North Korea from becoming a threatening nuclear power, with a firm commitment that the U.S. will not attack a peaceful North Korea...
I'd forgotten that Carter negotiated the 1994 accord; it rarely gets mentioned in the US media. Even the Bush administration, when they used to criticize that deal, omitted Carter's name. (They've stopped criticizing it.)
The Bush administration, as has been routine for them, has been incompetent in their management of North Korea. They seem to have a fundamental problem with seeing the world as others see it.
That said, even for a competent administration, North Korea would have been a hard problem to tackle. Now, with the failures of the Bush policies, it's much harder.
I can fully understand why NK wants a nuclear weapon; even before the crazed rhetoric of the neocons they knew the proven value of a nuclear deterrent. So even if they didn't have a very weird culture and a near-insane leader they'd want a nuclear weapon. What Carter doesn't address is that they also want to sell nuclear weapons; that would solve their cash flow needs.
Given their incentives to possess nuclear weapons, and their desire to sell them, I do have a hard time understanding why they'd give all that up. A promise not too invade can't be worth all that much. For one thing they'd never trust the US (who would?), for another that doesn't address their fundamental problem. They need much more than we can give them.
China is the key to North Korea, and China's export market is the key to China. It's time to offer China a deal -- either you deal with North Korea, or we withdraw from the WTO and put tariffs on Chinese goods. Sure, that would cause our economy to crater, but China would do down with us. As ugly as a world recession would be, it beats nuclear war on the Korean penninsula -- not to mention a nuclear strike on a US port. On the other hand, if China cooperates, we keep the spigots running, and spend our resources (aid, unemployment extensions, tax cuts, education credits, etc.) helping the US manufacturing sector fade gently into the night.