War isn't the best course of action here. Nor will it be the likely result of North Korea's renewed hostilites. We don't know all that much about NK, but what is known seems to indicate the thing they need most is food. The children growing up there now have been called "The Stunted Generation", because they don't have enough nutriants in their diets to reach full height. The effects of this childhood malnutrition will likely never leave them.
That is what should be focused on. South Korea has already cut all trade to NK. I really hope our own government dosen't trade with NK. Japan trading with NK seems unlikely, given the racial tension between the Koreas and Japan. This only really leaves China and humanitarian aid to help NK feed itself. If we wanted to be recklessly agressive about it, we could tell China that if they want their debt back, all trade with NK stops at once. It might work, it might not. We could also take a less agressive stance to stoping their trade with NK, but damned if I know what it could be. As for humanitarian aid, while I don't really like the idea of starving mislead people to destablize their oppresive government, NK has been getting more and more insane over the years. They need to go down soon, one way or another. It may be best to forcably keep aid organizations restrained in regards to NK for a while. Next, the DMZ should be heavly renforced to the point where a ground attack on it by the eventualy desprate NK would be utter suicide. If all of this can be done, and that isn't very likely, then North Korea would be starved to death. They would either collapse or give up, depending on potental rebellion groups and how far gone Kim-Jong-Il really is.