There's certainly more volatility ahead, perhaps as soon as Monday when markets reopen, and there are many reasons to worry. As Asia's biggest trading partner, China is wreaking particular havoc in emerging nations as its once-voracious demand for commodities declines. The mainland's $10 trillion economy, meanwhile, is a black box. No one outside President Xi Jinping's inner circle really knows how close China is to the brink, or what policy tools are being marshalled to avert a crisis