The causes and outcomes of the First Opium War between the UK and China.
The British Empire's grasp on the Americas was slipping right at the time when they needed those resources most. The massive amounts of tea they imported from China had created a huge trade deficit, but the Chinese were reluctant to let any Europeans trade outside of the Canton port strictly controlled by the Hong. So Britain sent a formal embassy led by Earl George Macartney.
Opium was illegal in China, but that didn't stop the East India Company from manufacturing it for the black market. The Chinese emperor appointed an official, Lin Zexu, to stop it. He seized and burned huge opium caches held by British merchants, and ultimately ordered the British out of China entirely. Instead, they set up base on a barren island that would become known as Hong Kong.
The British set up a blockade outside Canton, but one of their own private merchant ships tried to run through it. When the Chinese came to its defense, war began in earnest. Since the British had far superior firepower, they easily conquered Chuenpee and Chusan. Elliot and the Emperor's new envoy, Qishan, soon sought a treaty and agreed on generous terms... which their overseers harshly rejected.
The Chinese attempt to retake Canton by force failed. New British commanders took charge and would accept nothing less than total Chinese capitulation. They captured cities all the way up to Nanking, forcing the Emperor to negotiate. He had no choice but to accept an unequal treaty, kicking off a period of subservience to Europe which China still remembers today as the Century of Humiliation.