In late October 1839, the Thomas Coutts arrived in Canton. This ship was owned by Quakers who refused to deal in opium, and its Captain Smith believed Elliot had exceeded his legal authority by banning trade. The captain negotiated with the governor of Canton, signed the Qing legal bond, and agreed to unload his goods at Chuenpee, an island near Humen.

To prevent other British ships from following the Thomas Coutts, Elliot ordered a blockade of the Pearl River, and on November 3 the British Royal Navy ships HMS Volage and HMS Hyacinth fired warning shots at the British trading ship Royal Saxon as it attempted to sail to Canton.

The Qing navy attempted to protect the British merchant vessel, and reported a great victory for that day, though many Chinese ships were sunk by the British Navy in the resulting First Battle of Chuenpee.

In 1840, Elliot asked the Portuguese governor in Macau to let British ships load and unload their goods there in exchange for paying rent and any duties. The governor refused for fear that the Qing Government would discontinue supplying food and other necessities to Macau. On 14 January 1840, the Qing Emperor asked all foreigners in China to halt material assistance to the British in China. In retaliation, the British Government and British East India Company decided that they would attack Canton. The military cost would be paid by the British Government.

The China problem emerged just as Britain faced serious pressures in the Near East, on the Indian frontier, and in Latin America. Lord Palmerston, the British Foreign Secretary, supported the Opium War “to maintain the principle of free trade, obtain full compensation for the destroyed opium, and uphold Britain’s reputation.” The War was attacked in the House of Commons by William Gladstone, who denounced the war as "unjust and iniquitous" and criticised Palmerston's willingness "to protect an infamous contraband traffic."  The public and press in the United States and Britain expressed outrage that Britain was supporting the opium trade. Lord Palmerston replied by saying that the war was being fought to remedy Britain's balance of payments deficit. John Quincy Adams commented that opium was “incidental to the dispute... the cause of the war is the kowtow—the arrogant and insupportable pretensions of China that she will hold commercial intercourse with the rest of mankind not upon terms of equal reciprocity, but upon the insulting and degrading forms of the relations between lord and vassal.” 

In June 1840, an expeditionary force reached Canton from Singapore. The marines were headed by Commodore James Bremer, who demanded that the Qing Government compensate the British for losses suffered from interrupted trade. Following the orders of Lord Palmerston, a British expedition blockaded the mouth of the Pearl River, moved north and took Chusan. The next year, 1841, the British captured the Bogue forts that guarded the mouth of the Pearl River—the waterway between Hong Kong and Canton. By January 1841, British forces commanded the high ground around Canton and had defeated the Chinese at Ningbo and at the military post of Dinghai.

British military superiority drew on newly applied technology. British warships powered by steam were able to move against the winds and tides and support a gun platform with very heavy guns. In addition, the British troops were the first to be armed with modern muskets and cannons, which fired more rapidly and with greater accuracy than the antique Qing firearms and artillery. 

By the middle of 1842, the British had occupied Shanghai, thus controlling the critically important Yangtze River, and seized the tax barges, which transported tax revenue to the imperial court in Beijing. After a long string of humiliating defeats, which tarnished the reputation of Chinese imperial power, the war finally ended in August 1842, with the signing of the first of China's Unequal Treaties, the Treaty of Nanking. In the treaty, China was forced to pay an indemnity totaling 21 million silver dollars to Britain, open four ports to Britain, and cede Hong Kong to Queen Victoria“in perpetuity.” In the supplementary Treaty of the Bogue, the Qing Empire also recognised Britain as an equal and a “most favored nation” to China and gave British subjects extraterritorial privileges in treaty ports. In 1844, the United States and France concluded similar treaties with China, the Treaty of Wanghia and Treaty of Whampoa, respectively, initiating a century of “national humiliations” for the Chinese as concessions and new privileges were bestowed on the foreigners.

Legacy

The ease with which the British forces defeated the numerically superior Chinese armies seriously affected the Qing Dynasty's prestige. The success of the First Opium War not only allowed the British to resume the opium trade, but also paved the way to open the lucrative Chinese market to other commerce and to open Chinese society to missionary endeavors.

Lin Zexu, who had arrested 1,700 opium dealers and destroyed 2.6 million pounds of opium, was scapegoated for the military defeat. Nevertheless, Lin Zexu is popularly viewed as a hero of 19th century China, and his likeness has been immortalised at various locations around the world.

Daoguang’s death and legacy

Daoguang died on 25 February 1850, just as the upheaval of the Taiping Rebellion began to intensify, and was succeeded by his eldest surviving son. Daoguang had understood neither the intentions nor the determination of the Europeans, nor even the basic economics of the war on opium. Although the Europeans were outnumbered, outgunned and thousands of miles from home, they brought far superior firepower to bear wherever they attacked along the Chinese coast.