The Opium Wars, occurring in the mid-19th century, were primarily caused by British trade of opium in China, which led to widespread addiction and social problems. When the Chinese government banned opium imports, Britain responded militarily to protect its trade interests. The First Opium War (1839-1842) ended with the Treaty of Nanking, which ceded Hong Kong to Britain and opened several ports to foreign merchants. The Second Opium War (1856-1860) further expanded foreign influence in China. Outcomes included increased Western dominance, the weakening of Qing authority, and a series of unequal treaties that exploited China economically and politically.