North Korea has approximately fuck-all in the way of an effective delivery system. They want nukes for the same reason Iran does: a bargaining chip against the most severe sanctions and, failing that, a hedge against invasion. They know nuclear nations don't have to abide by the same rules as everyone else, because we and the Russians have proven that repeatedly. It's cheaper and easier for a destitute dictatorship like that to try and strong-arm their way to relevance with nukes than to try and build a functional infrastructure in the face of a crippling embargo. It's slightly more complex in the case of Iran, but generally speaking we might be the only ones who ever acquired nuclear weapons for predominantly offensive purposes. Once we popped the top on that can of worms, everyone else started pondering them simply as a means of survival.
