a war between Great Britain and China that began in 1839 as a conflict over the opium trade and ended in 1842 with the Chinese cession of Hong Kong to the British, the opening of five Chinese ports to foreign merchants, and the grant of other commercial and diplomatic privileges in the Treaty of Nanking.
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British Dictionary definitions for opium wars
two wars (1839–42; 1856–60) between China and Britain resulting from the Chinese refusal to allow the importation of opium from India. China ceded Hong Kong after the British victory in 1842. The British and French victory in the second war established free trade in Chinese ports and the legalization of the opium trade
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012