Excess

While talking about the population growth of the Qing empire, some simple arithmetic may skip your eyes.

It goes like this: By growing Champa rice, the productivity of farmland doubled. In other words, twice as many people could be fed - but the number of farmer needed remained the same. What happened to the people in excess?

In other words, how did they make a living?

Simple. By industry.

That's why the handicraft industry of the Qing empire, notably porcelain and textiles, had such an explosive development during that time. Thanks to Christopher Columbus and Ferdinand Magellan, international trade became a booming business, and there was no shortage of overseas market. Silk, china and tea were all in great demand by the Europeans, and, since Chinese people didn't quite need any imported goods, the Qing empire was running an astronomical surplus for some decades.

Of course, the wind changed when tea and opium were extensively planted in India - the latter served no purpose except being exported to China for the exchange of silver.

And the rest is history.