Weakness, thy name is Obama.
Logically speaking, North Korea can not hope for a weaker President or a weaker America than this moment. Anyone making that calculation would realize that circumstances will never be more in their favor. If North Korea does not attack now, while Obama is President, then we really never have to fear them at all, ever.
Add the fact that North Korea has nukes, while South Korea does not. Millions of starving North Koreans. Lots of food just across the border. New North Korean prince who has some spurs to earn. And the early intel the SK's got on the artillery attack that occurred last week, was that the NK were going to shell all 5 disputed islands. Don't think you need to be a rocket scientist to see where this one is headed.