The First Opium War or the First Anglo-Chinese War was fought between the British East India Company and the Qing Dynasty of China from 1839 to 1842 with the aim of forcing China to allow free trade, particularly in opium. The Treaty of Nanjing, first of the unequal treaties, granted an indemnity to Britain, opening of five Treaty Ports, and the cession of Hong Kong, ending the monopoly of trading in the Canton System. The wars are often cited as the end of China's isolation and the beginning of modern Chinese history.

The war was denounced in Parliament as unjust and iniquitous by young William Ewart Gladstone, who criticised Lord Palmerston's willingness to protect an infamous contraband traffic. Outrage was expressed by the public and the press in America and England as there was a perception that British interests may well have been simply supporting the drugs trade.