OPIUM WAR: The war between Great Britain and CHINA (1839-1842) forced CHINA to expand trade opportunities to Great Britain and cede HONG KONG. The war began over CHINA's failure to block the import of opium to the country by European traders. The imperial government attempted to bar all trade with the West, and Great Britain responded by declaring war on the country. As a result, opium continued to be exported to CHINA, causing the decline of the educated classes. (See also China article).