March 3, 1857 – France and the United Kingdom declare war on China
Opium Wars, two armed conflicts in China in the mid-19th century between the forces of Western countries and of the Qing dynasty, which ruled China from 1644 to 1911/12. The first Opium War (1839–42) was fought between China and Britain, and the second Opium War (1856–60), also known as the Arrow War or the Anglo-French War in China, was fought by Britain and France against China. In each case the foreign powers were victorious and gained commercial privileges and legal and territorial concessions in China. The conflicts marked the start of the era of unequal treaties and other inroads on Qing sovereignty that helped weaken and ultimately topple the dynasty in favour of republican China in the early 20th century.
The Second 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 Arrowwhile 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.
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. – Encyclopedia Britanica