While the global economic crisis has changed our lives in the US, it has really put a crunch on other nations that are in the real poverty zone. When it comes to poverty, it's difficult to compete with a communist nation, because you have an economic system designed by a maggot-infested hippie who never worked a day in his life, and let 4 out of 7 of his own children starve to death while living in the slums of London at the expense of a family who made their money using the system he despised. If you model your nation's economic system after this dirtiest of dirtbags, you will see similar proportions of the population suffer the same fate Karl Marx's children did on London's East End, while the Engel's family foot the bill.
Such is the case with North Korea. Just look at satellite imagery of the place compared to South Korea:
With the economic downturn affecting 3rd world dirt-holes with food shortages, and the natural calamities that hit Japan, you have 2 of North Korea's main food suppliers forced to focus on internal domestic crises with regard to energy, finance, population, pensions, etc. This naturally would place North Korea on an even worse suckfest akin to the Engel's evicting hippie Marx and his family. One can only imagine the unrest going on in North Korea right now as the people look to this goon as "dear leader":
China can't afford for North Korea to collapse under un's rule, but there is only so much they can do. He is also faced with the real impact of the global economy, and lashing out is the only card he's got really. If he were to play the nice guy and beg for more foreign aid openly, in exchange for putting away his nuclear toys, it would appear as weakness to his people and the regional powers, but more important is his image to the NORKs. It also is better for China because if the natural & inevitable collapse of North Korea were to occur now, China would be faced with hordes of untrained communist peasants with no skills to speak of, in an already extreme case of over-population in mainland China.
North Korea has a population of over 24 million doomed souls who would jump ship as soon as the communist state failed. South Korea and Japan are in the same boat-the last thing they want is a bunch of dead beats pouring over their borders to flood their already excess labor markets. Saber-rattling is the only thing that makes sense for everyone in the region in that regard.