I think that china is using North to **** off America... they dont want to do it directly so not to taint their public image... I dont believe that north decides to shell south or threaten USA with nuclear weapons without the "Big Dragon" behind their back... China has massive military with quite decent armament, it is by no means worse than Russians, since china pretty much have been copying russian equipment since the time of USSR... It took everyone decades to make 5th generation fighter jet... China made it randomly out of stolen technologies from both USA and Russia... and they couldn't care less about patents... They are not using their military anywhere in the world at this moment... surely there is no point having such great army with no use.
http://en.wikipedia.org/wiki/Chengdu_J-20 (5th jen fighter)
Uk has pretty small army and yet we manage to stick our noses everywhere... Afghanistan,Libya, Africa....
China is going to go bonkers sooner or later, they already essentially wrote mein kempf saying what territories they think belong to them... now its just a waiting game.
If war breaks out in Korea, I cant see China nor Russia just giving up north Korea to USA.. It will be a pretty global conflict but it would not be direct, same as last korean war... 90% of those Migs flown by "north Koreans" were actually Soviet Pilots and its openly admitted now, there is even a list in wikipedia with names and ranks and how many aircraft were downed by individuals.
http://en.wikipedia.org/wiki/List_of_Korean_War_flying_aces
Given the worlds current state, we need another war... and I dont see why a localised Korean war would be impossible, maybe with few nukes going off in that area of the world... But I dont see full nuclear war raging, since that would be in no ones interest.