Riots in China is as common as shooting in the states. For a country as big as China, you can find riots almost everyday. But it doesn't mean a melt down.
However, I think the most danger in China is that there may be a armed conflict between China and Taiwan. That may lead to war, hot or cold between China and the US. That may be very bad for the stock market. But it may be good for oil fields and metal mines in the North America.
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