Final answer:
Britain became the dominant economic power in China after the Opium Wars, exerting control over trade and gaining influence through unequal treaties, including the Treaty of Nanjing.
Step-by-step explanation:
After the Opium Wars, which saw China defeated by foreign powers, the dominant economic power in China was Britain. Through the Treaty of Nanjing in 1842, at the end of the First Opium War, and subsequent treaties following the Second Opium War, Britain along with other Western powers such as France, Russia, and later Japan, established spheres of influence in China. These treaties forced China to open up to foreign trade under unequal terms and granted Britain control over Hong Kong and other aspects of Chinese sovereignty. As a result of these concessions, Britain became the most influential foreign power in China, leveraging its strong economic relationship to exert control over trade and other affairs within the region.