...cut off their access to oil from the Middle East, resources from Africa, or food from wherever, China will be in real trouble.
The powers around China could effectively block all shipping in and out of China. The thing to remember is China is not a self sustaining nation. Cut off western money flow, cut off raw material, cut off exports and China is a nation of a Billion people with no way to feed themselves.
Why, two reason corruption from top down and central planning from top down. Now if China was a true capitalist country I would be worried because they do have the ability to be powerful, but with the level of corruption it will not happen (without aid from Western Leaders).
China has large and expanding pipeline capacity with their friendly neighbor, the second largest oil exporter in the world. As for cutting them off from trade with the rest of the world, good luck. I suspect the Chinese leaders can read a map as well as westerners can.