Which situation led to the defeat of China in the Opium War (1839-1842)?

Opium Wars, two armed conflicts in China in the mid-19th century between the forces of Western countries and of the Qing dynasty, which ruled China from 1644 to 1911/12. The first Opium War (1839–42) was fought between China and Britain, and the second Opium War (1856–60), also known as the Arrow War or the Anglo-French War in China, was fought by Britain and France against China. In each case the foreign powers were victorious and gained commercial privileges and legal and territorial concessions in China. The conflicts marked the start of the era of unequal treaties and other inroads on Qing sovereignty that helped weaken and ultimately topple the dynasty in favour of republican China in the early 20th century

Explanation:

cultural/diplomatic relations. most medieval japanese   culture has chinese origins. writing, architecture etc.