[yeukhon]

This has never been a size problem. China can probably build a human bridge all the way to SF with that population (I am probably exaggerating), but that doesn't mean the Chinese will win. You can tell this from modern warfares (Vietnam, Iraq etc). Size and advancement in tech can get us to the winning zone for sure, but we cannot discount locals' discomfort, loyalty and nationalism.

[viraptor]

Slightly off topic, but I just had to check: Shanghai to SF is around 9873.51 km. Some internet counter estimates China's population at 1,389,221,780. Assuming 50/50 split (can't find a better one now), average height in China is 161.45 cm. That gives us a possible human chain 2 242 898.56 km long. That's more then enough to reach from China to SF.