In China, the Qing dynasty Qianlong Emperor wrote to King George III in response to the MaCartney Mission's request for trade in 1793: "Our Celestial Empire possesses all things in prolific abundance and lacks no product within its borders. There is therefore no need to import the manufactures of outside barbarians in exchange for our own produce." Tea had to be paid in silver bullion, and critics of the tea trade at this time would point to the damage caused to Britain's wealth by this loss of bullion. As a way to generate the silver needed as payment for tea, Britain began exporting opium from the traditional growing regions of British India (in present-day Pakistan and Afghanistan) into China. Although opium use in China had a long history, the British importation of opium increased fivefold between 1821 and 1837, and usage of the drug became more widespread across Chinese society. The Qing government attitude towards opium, which was often ambivalent, hardened because of the social problems created by drug use and took serious measures to curtail importation of opium in 1838–39. Tea had become an important source of tax revenue for the British Empire, and the banning of the opium trade and thus the creation of funding issues for tea importers was one of the main causes of the First Opium War.