The First Opium War (), also known as the Opium War or the Anglo-Sino War was a series of military engagements fought between the British Empire and the Qing dynasty of China between 1839 and 1842. The immediate issue was the Chinese enforcement of their ban on the opium trade by seizing private opium stocks from merchants at Canton and threatening to impose the death penalty for future offenders. Despite the opium ban, the British government supported the merchants' demand for compensation for seized goods, and insisted on the principles of free trade and equal diplomatic recognition with China. Opium was Britain's single most profitable commodity trade of the 19th century. After months of tensions between the two nations, the British navy launched an expedition in June 1840, which ultimately defeated the Chinese using technologically superior ships and weapons by August 1842. The British then imposed the Treaty of Nanking, which forced China to increase foreign trade, give compensation, and cede Hong Kong to the British. Consequently the opium trade continued in China. Twentieth-century nationalists considered 1839 the start of a century of humiliation, and many historians consider it the beginning of modern Chinese history.
In the 18th century, the demand for Chinese luxury goods (particularly silk, porcelain, and tea) created a trade imbalance between China and Britain. European silver flowed into China through the Canton System, which confined incoming foreign trade to the southern port city of Canton. To counter this imbalance, the British East India Company began to grow opium in Bengal and allowed private British merchants to sell opium to Chinese smugglers for illegal sale in China. The influx of narcotics reversed the Chinese trade surplus, drained the economy of silver, and increased the numbers of opium addicts inside the country, outcomes that seriously worried Chinese officials.
In 1839, the Daoguang Emperor, rejecting proposals to legalise and tax opium, appointed Viceroy Lin Zexu to go to Canton to halt the opium trade completely.