During the time period from 1839 to 1842, there was corruption in China with Britain. These times were called, "The Opium Wars." Chinese allowed the British to access trade in the port of Canton. In China, tea was grown, and Britain was the buyers. They thought they needed to balance the trade and sell things back to China in exchange for the tea. So Britain introduced Opium. Opium is a drug grown in India, it's addicting and used in many strong medicines.
Then in 1838, further efforts to trade opium were ended, and anyone who was trying to trade it would be killed. British merchants went to China on thier ships with guns destroying the coastal cities and the wars had begun. China was unprepared for the attack and was defeated. Forced to sign the Treaty of Nanjing in 1842, and the British supplementary Treaty of the Bogue in 1843. More ports were open to trading with the British in China.