Uh, funny how you make a little comment and you find a whole thread the next day :)

So, ok. My comment was a bit too concise for its own good. I wasn't thinking of a geopolitical breakdown à la USSR but of rampant arnarchy with a destabilized/delegitimized central government. In itself, it would a Sino-Chinese problem and none of our business. The real issue would be that the central power would probably try to restore its hold by upping the ante, for instance to turn to ultra-nationalism and militarism.

And BTW, China has not been united for the past 5,000 years. Its history is much more complex with many invasions and a succession of foreign rulers. To the point that many things we consider as typically Chinese are actually Manchu, brought fairly recently (17th century AD) by the Qing, the last imperial dynasty.

The main theme of China's history is this permanent fight between centralized power and centrifuge forces, splitting the country apart. You need to know that if you want to understand a bit the utter strangeness that sometimes surrounds the relations between the PRC and Taiwan.