So China's quite the middle guy between North and South Korea, huh? After either one of the Korea get eliminated, China might fight over the NK/SK, depending which side has lost their leader. Oh, what's China's reason to fight over the lands? Well, the Ancient Korea was a colony of China, knowing China they'll argue for the sake of it. Lol
China's armies haven't really reached that level yet, though undeniably they are improving. If a war between China and Russia happens, (basing on current standards) Russia wins but definitely not an easy one.