China's biggest problem, besides the mountains of debt, the record inequality, the broken farming (in which ~600 million people are being kept busy with intentionally inefficient farming practices so they have something to do), the lack of individual freedom, the lack of property rights for farmers, the pollution, and the heated conflicts with most of their neighbors - is probably water. 20% of the world's population, 5% to 6% of the world's fresh water, and falling:

http://qz.com/166235/chinas-water-shortage-is-so-bad-it-coul...