What damaged the relationship between Great Britain and China during the mid-19th century?

The relationship between Great Britain and China was severely damaged during the mid-19th century primarily due to the Opium Wars. There were two Opium Wars—the First Opium War (1839-1842) and the Second Opium War (1856-1860).

The main cause of tension was the trade imbalance between Britain and China. China was exporting valuable goods like silk, tea, and porcelain to Britain but was not equally interested in British goods. To correct this imbalance, British merchants began to illegally import opium, grown in India, into China. Opium addiction became rampant, and the Chinese government, concerned about the social and economic impact, confiscated and destroyed over 20,000 chests of opium in 1839.

This act was the catalyst for the First Opium War, as Britain sought compensation for the destroyed opium and desired to open China to British trade. The superior British military might forced China to surrender, resulting in the Treaty of Nanking in 1842, which heavily favored British interests. China was forced to cede the island of Hong Kong to Britain, open up several ports to British trade, grant extraterritorial rights to British subjects, and pay a large indemnity.

The Second Opium War broke out over further disputes, including the British desire for more trading rights, legalisation of the opium trade, and the treatment of British envoys. The war ended with the Treaty of Tientsin and the Convention of Peking, which further opened China to Western trade and influence, exacerbating China's internal issues and resentment towards foreign powers.