The Second Opium War, or arrow war broke out following an incident in October 1856 during which Chinese officials boarded a vessel by the name of Arrow. The crew was put under arrest for smuggling and piracy. The Chinese were then accused of tearing down and vio;ating the british flag during inspection. The war started when British forces attacked Guangzhou in 1856.
The french than joined the british after one of their missionarys were killed by a local Mandarin in China. Hostilities broke out once more in 1859 after China refused to establish a British embassy in Beijing as had been promised by the Treaty of Tianjin. Fighting erupted both in Hong Kong as well as Beijing, where the British set out to destroy the summer palace and the old summer palace. Hostilities broke out once more in 1859 after China refused to establish a British embassy in Beijing as had been promised by the Treaty of Tianjin in 1860 ending the war.

A typical opium den

In March1839, the Emperor appointed a new strict Confucianist commissioner, Lin Zexu to control the opium trade at the port of Canton. His first course of action was to enforce the imperial demand that there be a permanent halt to drug shipments into China. On 27 March 1839 Charles Elliot, British Superintendent of Trade, demanded that all British subjects turn over their opium to him, to be confiscated by Commissioner Lin Zexu, amounting to nearly a year's supply of the drug. After it was surrendered, trade between them restarted under the strict condition that no more drugs would be brought into China. Lin Zexu had all British merchants sign a bond promising not to deal opium or they would be killed. They oposed signing this bond. So Lin had the opium disposed of dissolving it in water, salt, and lime, and dumping it into the ocean. The British Government said Lin was destroying their property and when they heard what was happening in Canton they sent a British Indian army that arrived in June 1840.
This lead to the first opium war. The British had a powerful fleet of steam engine warships were not only virtually indestructible but also highly mobile and able to support a gun platform with very heavy guns. The Chinese ships were not nearly as powerful and were destroyed. Now the British were destoying towns and trade barges. In 1842 the treaty of Nanjing, Bogue, Wanghia, and Whampoa were signed and ended the first opium war.

Following the battle of Plassey in 1757, the British East India Company pursued a monopoly on production of Indian opium. For the next 50 years opium trade would be the key to their subcontinent. Importing opium to the Chinese was actually illegal by the Chinese law. So the East India Company established an elaborate trading scheme partially relying on legal markets, and partially leveraging illicit ones. They would bring in opium hidden on British ships then smuggled into China. British exports of opium into China grew from 15 tons in 1730, to 75 tons in 1773. In 1799 the Chinese empire reinstated the ban on opium.