Actually it would make more sense if China performed a regime change on North Korea. One they could stabilize the region while keeping a communist government in place as a buffer between the West without inciting Japan to fully re-arm itself and a messy Korean unification under America's sphere of influence. If anything they could then undermine South Korea by installing the mantra of manipulating their own currency and using cheap labor and the West's ability to sell themselves out for crap products made cheaply. Nukes, hell cheap iPads will win you beach side property next to Dennis Rodman in NewPort Beach without even shooting a bullet.