2nd Opium War: In the mid-1850s, while the Qing government was embroiled in trying to quell the Taiping Rebellion(1850–64), the British, seeking to extend their trading rights in China, found an excuse to renew hostilities. In early October 1856, some Chinese officials boarded the British-registered ship Arrow while it was docked in Canton, arrested several Chinese crew members (who were later released), and allegedly lowered the British flag. Later that month a British warship sailed up the Pearl River estuary and began bombarding Canton, and there were skirmishes between British and Chinese troops. Trading ceased as a stalemate ensued. In December Chinese in Canton burned foreign factories (trading warehouses) there, and tensions escalated. Read about the First Opium War.
The French decided to join the British military expedition, using as their excuse the murder of a French missionary in the interior of China in early 1856. After delays in assembling the forces in China (British troops that were en route were first diverted to India to help quell the Indian Mutiny), the allies began military operations in late 1857. They quickly captured Canton, deposed the city’s intransigent governor, and installed a more-compliant official. In May 1858 allied troops in British warships reached Tianjin(Tientsin) and forced the Chinese into negotiations. The treaties of Tianjin, signed in June 1858, provided residence in Beijing for foreign envoys, the opening of several new ports to Western trade and residence, the right of foreign travel in the interior of China, and freedom of movement for Christian missionaries. In further negotiations in Shanghai later in the year, the importation of opium was legalized.
End of the 2nd Opium War: The British withdrew from Tianjin in the summer of 1858, but they returned to the area in June 1859 en route to Beijing with French and British diplomats to ratify the treaties. The Chinese refused to let them pass by the Dagu forts at the mouth of the Hai River and proposed an alternate route to Beijing. The British-led forces decided against taking the other route and instead tried to push forward past Dagu. They were driven back with heavy casualties. The Chinese subsequently refused to ratify the treaties, and the allies resumed hostilities. In August 1860 a considerably larger force of warships and British and French troops destroyed the Dagu batteries, proceeded upriver to Tianjin, and, in October, captured Beijing and plundered and then burned the Yuanming Garden, the emperor’s summer palace. Later that month the Chinese signed the Beijing Convention, in which they agreed to observe the treaties of Tianjin and also ceded to the British the southern portion of the Kowloon Peninsula adjacent to Hong Kong.