In 2015, a picture of a Chinese fruit vendor trading stocks with a laptop at his stall went viral on social media. The number of Chinese with margin trading accounts — in which investors are extended huge amounts of credit to bet with — had exploded so far that even street-market grocers felt it was normal to place leveraged bets on equities.

It became a bit of a symbol of the economic and financial turmoil in China and much of the rest of the developing world: Growth has slowed, but debt is sloshing around like never before.

Goldman Sachs recently published a piece of research that boldly described events in the world's emerging markets, or EM, as the "third wave" of the financial crisis that began in 2008.

The first wave was the US subprime-housing crisis, and the second wave was the eurozone sovereign-debt crisis.