The First Opium War, also known as the Opium War or the Anglo-Chinese War, is a series of military engagements fought between the United Kingdom and the Qing dynasty of China over diplomatic relations, trade, and the administration of justice in China.

In the seventeenth and eighteenth centuries, the demand for Chinese goods (particularly silk, porcelain, and tea) in Europe had created a trade imbalance between Qing Imperial China and Great 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 auction opium grown in India to independent foreign traders in exchange for silver, and in doing so strengthened its trading influence in Asia.

This opium was transported to the Chinese coast, where local middlemen made massive profits selling the drug inside China.

The influx of narcotics had reversed the Chinese trade surplus, drained the economy of silver, and increased the numbers of opium addicts inside the country, outcomes that worry Chinese officials.

In 1839, the Daoguang Emperor, rejecting proposals to legalize and tax opium, appoints viceroy Lin Zexu to solve the problem by completely banning the opium trade (various forms of opium had been prohibited in China since 1729) without offering compensation and ordered a blockade of foreign trade in Canton.

Lin had confiscated 20,283 chests of opium (approximately 1210 tons or 2.66 million pounds) after confining the foreign traders to the Canton Factories and cutting off their supplies.

The British government does not question China's right to prohibit opium, but it objects to the way this is handled; it views the sudden strict enforcement as laying a trap for the traders, and the confinement of the British with their supplies cut off is tantamount to starving them into submission or death.

They dispatch a military force to China and in the ensuing conflict, the Royal Navy uses its naval and gunnery power to inflict a series of decisive defeats on the Chinese Empire, a tactic later referred to as gunboat diplomacy.

In 1842, the Qing dynasty is forced to sign the Treaty of Nanking—the first of what the Chinese will later call the unequal treaties—which grant an indemnity and extraterritoriality to Britain, open five treaty ports to foreign merchants, and cede Hong Kong Island to the British Empire.

The failure of the treaty to satisfy British goals of improved trade and diplomatic relations leads to the Second Opium War (1856–60), and the perceived weakness of the Qing dynasty results in social unrest within China, namely the Taiping Rebellion.

In China, the war is considered the beginning of modern Chinese history.