We have been threatening military action through several presidents-- all without success except that NK kept building up its arms and nuclear capability. Today, NK's weapons capability has expanded their ability to counter attack any attack by the US almost as soon as it begins. This is a difficult negotiation-- the costs of our attacking and retaliatory attack by NK (just by non-nuclear missiles and 10's of thousands of heavy artillery and rockets) would be a huge, huge cost in lives, and destruction in South Korea and to some extent Japan. But we do not want to pay what would be an amount equal to our losses to North Korea to gain their agreement and compliance. We want to avoid a "war" and de-nculearize NK and we will pay for that in trade arrangements, foreign aid, and removing weapons and troops-- but we do not want to offer, let alone pay, until we know NK is willing to adhere to our terms. Tough negotiating problem because we want China to pay part of the price too.