Opium Wars
China was forced to sign the Treaty of Nanking and Treaty of the Bogue. This forced China to open up some of its ports for trade to Western countries, not just Great Britain.  British people in China also received the right of extraterritoriality, meaning when accused of crime they could be tried by their own officials rather than those of China. Finally, China had to give up Hong Kong Island, which became a British colony. Britain had nothing to give back in return, and so these treaties became the first of those known as the "unequal treaties".  Other Western countries soon signed similar treaties with China.