The Second Opium War was fought between 1856 and 1860, which was about ten years after the First Opium War, and it pitted China against both Britain and France. Once again, the Chinese were defeated, and further concessions were granted to the Europeans. Within China, many people were angry not only at the Europeans but also at their government, which they began to see as weak and incompetent.

France complained about the preferential status given to Britain by the Treaty of Nanking and insisted that China open up ports in China for French merchants to use. In 1844, China acquiesced and signed the Treaty of Whampoa. Five ports were opened to them, and as compensation, China was allowed to charge a tariff. The French also used that opportunity to persuade China to permit the presence of Catholic missionaries in China. In 1846, the Daoguang Emperor signed an edict allowing the Chinese to convert to Catholicism if they so wished. Despite that, a French missionary, Father Auguste Chapdelaine, was arrested by a Mandarin bureaucrat for causing unrest and was eventually executed. France was infuriated and sent out ships filled with forces.

Simultaneously, the British had been campaigning for the legalization of opium in China. The opportunity presented itself in 1856 when the Chinese seized a British ship, the Arrow, on charges of piracy for the illegal shipment of opium inside China. Ye Mingchen, the Chinese official, arrested the captain and the crew and took possession of the ship, saying that they only did so because the registration had expired.

Soon after this incident, the French allied themselves with Britain, and they attacked Canton. The Second Opium War officially broke out by this point, although it is clear that tensions had been simmering for some time. In 1858, the French and British managed to finally capture Canton. They also captured Ye Mingchen and exiled him to Calcutta, India. The Chinese attacked a US Navy steamer at the mouth of the Peiho River in Tientsin, and the Americans retaliated by attacking and capturing Chinese forts on the Pearl River. The Xianfeng Emperor was, at the time, embroiled in the Taiping Rebellion and his resources were becoming thin. He was forced to succumb to Western pressures and sought peace by way of the Treaty of Tientsin.

Russia and China had border disputes in the prior century, but in 1858, China negotiated an ancillary treaty, the Treaty of Aigun, because they couldn't afford to start another conflict.