Im pretty sure that if China went to war (on two fronts) they would have a revolution behind their back in a year's time. Weather or not it would be successful or not, I dont know, but it would be a thorn in their side. My guess is that it would start in the western regions amongst the Muslim population.
There was actually a violent riot in one of the southern provinces some years ago because the police were confiscating fertility drugs. Judging from the aftermath it looks like explosives were used.