where did the war originate?
China.
Second Opium War
The war followed on from the First Opium War. In 1842, the Treaty of Nanjing—the first of what the Chinese later called the unequal treaties—granted an indemnity and extraterritoriality to Britain, the opening of five treaty ports, and the cession of Hong Kong Island. The failure of the treaty to satisfy British goals of improved trade and diplomatic relations led to the Second Opium War (1856–60). 
what is cragside? A Victorian country house. where is it located? Near the town of Rothbury in Northumberland. how is the house and armstrong connected? It was the home of William Armstrong, 1st Baron Armstrong. what is the architectural style of the house? Tudor revival style. what was armstrong's profession? An engineer and an industrialist. was he supportive of weapons? He was the founder of an armament firm and supported weapons. has he designed any weapon? Yes, the Armstrong gun. where were they used? It was used in the Second Opium War. did he manufacture it or somebody else did? Elswick Ordnance Company and the Royal Arsenal manufactured it.
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Second Opium War [SEP] Origins of the war
The war followed on from the First Opium War. In 1842, the Treaty of Nanjing—the first of what the Chinese later called the unequal treaties—granted an indemnity and extraterritoriality to Britain, the opening of five treaty ports, and the cession of Hong Kong Island. The failure of the treaty to satisfy British goals of improved trade and diplomatic relations led to the Second Opium War (1856–60). In China, the First Opium War is considered to have been the beginning of modern Chinese history. Between the two wars, repeated acts of aggression against British subjects led in 1847 to the Expedition to Canton which assaulted and took, by a "coup de main", the forts of the Bocca Tigris resulting in the spiking of 879 guns.