Great Britain won the Opium War against China. Their victory created foreign spheres of influence in China, allowed Great Britain to take possession of Hong Kong, opened China to European influence and created a drug epidemic in southeastern Asia.
The Opium Wars began over a trade dispute between China and Great Britain. British merchants wanted tea, which at the time, could only be purchased in China. China refused to trade with the British except in silver, creating a trade imbalance. The British reversed the imbalance by smuggling opium into China. China responded by arresting British traders and confiscating the opium. The British retaliated by capturing Shanghai and the Yangtze River. In 1842, they forced China to sign the Treaty of Nanking, which opened their cities to trade and relinquished Hong Kong to Britain. Hostilities broke out again in 1856, which forced China to accept European control of its coastal cities.