The only way Kim can leverage his weaker military power is by making his opponents believe he may be crazy enough to launch a war anyway. This strategy not only allows Kim to deter foreign attacks, but also gets him the maximum concessions in talks to give up the nuclear bomb.
Because the other negotiating nations believe the threat Kim would use nuclear weapons cannot be ruled out, they are prepared to offer much more to remove this risk. By signaling that he is irrational and unpredictable, Kim can turn a weak set of cards into a winning hand.
Washington and its allies face the opposite problem -- they are unable to make Kim believe their threats are credible.So while Kim remains leader of North Korea, the country will remain a constant source of regional scares. Kim's strategy has repeatedly won him concessions, and also helps him maintain his internal grip on power. There is no reason for him to throw away his best cards.