A colonial-era building in Shamian in Guangzhou, where a Western concession was set up in 1861 after the Qing defeat in the Second Opium War. [Photo by Satarupa Bhattacharjya/China Daily]

Gateway Canton

In the 18th century, Britain was buying tea, porcelain ware and silk from China while selling woolens, watches and forks. But the trade surplus emerged in China's favor. For a while Britain also sold cotton to China but the import fell due to China's own fiber plantations.

By many accounts, that's when opium entered the picture.

To reduce the trade deficit, British merchants "dumped" opium on the Chinese market, according to an exhibit at the Opium War Museum.

"If they wanted to balance the trade they had to bring China something, but they didn't have the products," Wu says.

In the immediate decades before the first phase of the opium wars, an estimated 20,000 boxes (60 kilograms in each) were being annually transported to China. A box of opium would sell between 500 and 800 taels (ancient Chinese currency) of silver in Canton, much higher than what it cost in colonial India.