First off, they have acquired much of our technology and weapons systems, both overty and coverty. They have sunburn missiles that are designed to destroy US aircraft carriers. They have enough nukes to make a difference, and they have the means to deploy them successfully.
They have MANY of our manufacturing plants, ranging from semiconductor plants such as Intel's, down through the spectrum of products such as shoes and clothes. Are there any shoe or textile plants still in the US?
They invented the Art of War, and know Sun Tzu better than us. They've prepared and planned for a war with the US for decades. In fact, I'm sure you're aware of the numerous articles on that subject. The below link is just an example;
Pentagon study finds China preparing for war with U.S
Don't you suppose China may just be following Sun Tzu, and have always been planning to take over the US? What of the Panama Canal? What of COSCO? What of the bases in the Pacific and even in the Bahamas?
Perhaps the whole sharade will play out when and if we decide to invade Iraq. Once we are involved in a major conflict there, as well as occupied in Bosnia, Afghanistan, and elsewhere, who's going to be left to defend the US? What if North Korea is in league with China and attacks South Korea? What if China attacks Taiwan? Then what?
What would Pakistan do? Nuke India maybe?
Do you see that the possibilities are profound, and that we need to give this some REALLY serious thought?
For the time being however, we buy all of their stuff. Without us they'd be toast.... really. They need us desperately right now, or it all comes crashing down. Just go to Wal-Mart and read tags and you'll see what I mean.