Ask a well-educated person which country boasts the largest equity market and you’ll usually get the right answer: the United States. Ask which country has the second largest market and you’re likely to get a range of answers: Japan? Britain? Germany?

The answer is China. In terms of annual trading volume, China's equity market has been #2 since 2009. Measured by total market capitalization, it has been #2 for seven of the past nine years....

Why should this matter now? First, because it highlights the extraordinary spread of market-based finance in a country led for more than 65 years by its communist party.... Second, because the growth in Chinese equity markets comes with sizable risks. Recent experience drives home this point....