The British East India Company had been buying Chinese tea, silk, and porcelain at the Canton trade depot since the late 17th century. The trade was one-sided — Chinese demand for British goods was minimal, while British demand for Chinese exports was — and produced an annual silver trade deficit of approximately £2 million by the 1820s.

The Company’s solution was opium. Indian poppy production under Bengal Company monopoly had been expanded from the 1780s. The opium was exported to China through Canton, sold to Chinese smugglers (because Chinese import was illegal), and produced silver flows that reversed the trade balance. By 1838 approximately 1,400 tonnes of British opium were entering China annually. The Chinese addiction population was estimated at 12 million.

Lin Zexu

The Qing Daoguang Emperor appointed the senior imperial scholar Lin Zexu in December 1838 as Imperial Commissioner with extraordinary authority to suppress the opium trade. Lin reached Canton on 10 March 1839. He ordered the British opium merchants to surrender their stocks within three days under threat of military force.

The British Superintendent of Trade Charles Elliot — caught between the Chinese ultimatum and the British merchants’ refusal to surrender voluntarily — formally requisitioned the British opium stocks in the name of the British government and turned them over to Lin. The volume was approximately 1,200 tonnes — about £2 million in 1839 prices, approximately £240 million in 2025 money.

Lin destroyed the opium in public over 23 days in June 1839 at Humen on the Pearl River. The opium was mixed with lime and salt water in long trenches, dissolved, and flushed into the river. The destruction was public theatre — Lin wrote a public apology to the sea god for the contamination — and was a humiliation of the British commercial presence.

The British response

The British government under Foreign Secretary Lord Palmerston decided in October 1839 to use military force to extract compensation for the destroyed opium and to force the legalisation of the opium trade. The justification was the British constitutional principle that the Crown was required to defend British property abroad. The opium trade’s moral status — the Chinese government had explicitly outlawed it as a public-health measure, and the British government’s knowing facilitation of the smuggling was already controversial in British parliamentary debate — was not relevant to the legal-diplomatic case.

The British expeditionary force of approximately 5,000 troops and 16 warships, plus 4 of the new steam-powered iron-hulled gunboats including the Nemesis (commissioned 1839, the first ocean-going iron warship), arrived off Canton in June 1840. The campaign that followed across 1840-1842 was asymmetric.

The British naval and military technology — Congreve rockets, percussion-cap muskets, iron-hulled steam gunboats with shallow draft that could navigate the Chinese river systems — was a generation more advanced than the Qing equipment. The Qing army was equipped with matchlock muskets and bronze cannon dating from the 17th century. The Qing navy was wooden junks. The technological gap had not been visible during the previous 200 years of Sino-European contact because direct military confrontation had been rare.

The British forces took the Pearl River forts (August 1840), seized Chusan (July 1840), captured Canton (May 1841), captured Amoy (August 1841), captured Ningbo (October 1841), and captured Shanghai (June 1842). The decisive engagement was the British force’s August 1842 advance up the Yangtze to Nanking, which was the Qing dynasty’s secondary capital and the location of imperial tombs. The Qing government sued for peace.

The Treaty of Nanking

The Treaty of Nanking was signed on 29 August 1842 aboard HMS Cornwallis in the Yangtze. Its principal terms were:

— Cession of Hong Kong Island to Britain in perpetuity — Opening of five treaty ports (Canton, Amoy, Foochow, Ningbo, Shanghai) to British residence and trade — Indemnity of £21 million silver (12 million Spanish silver dollars equivalent) payable over four years — Abolition of the Cohong monopoly trade system — Most-favoured-nation status for British trade

The legalisation of the opium trade — which had been the original British objective — was not included in the Treaty of Nanking. It was achieved through the supplementary Treaty of the Bogue in October 1843.

The treaty was the first of the Unequal Treaties that the Qing dynasty would sign with European powers across the subsequent 60 years. The structural concessions — extraterritorial legal jurisdiction for British residents, fixed tariffs that China could not unilaterally adjust, military garrison rights at the treaty ports — constrained Chinese sovereignty for the entire late-Qing period.

What followed

Lin Zexu was exiled by the Daoguang Emperor to the western Xinjiang frontier as punishment for the diplomatic disaster. He served at Ili from 1842 to 1845, was pardoned in 1845, and died of natural causes at Chaozhou in 1850, aged 65. His reputation in modern Chinese historiography has been rehabilitated since the early 20th century — he is now treated as a hero of anti-imperial resistance rather than as the failed official who provoked the war.

The Second Opium War (1856-1860) extended the British and French concessions further; the 1860 Anglo-French expedition to Beijing burned the Old Summer Palace. The Qing dynasty entered the late-19th-century structural decline that would culminate in the Boxer Rebellion and the 1911 Xinhai Revolution.

Hong Kong Island remained a British colony until 1 July 1997, when it was returned to Chinese sovereignty under the terms of the 1984 Sino-British Joint Declaration. The treaty cession of 1842 — which had been “in perpetuity” — lasted 155 years.