Spent few hours reading about the 1997 return of Hong Kong to China. Transfer of sovereignty of Hong Kong.
Some interesting notes: Unequal treaty.
Margaret Thatcher claims that these are international treaties and should be repected. The brit empire tries to sell Opium to chinese, see Opium war, when chinese lost the war, the brit declared these treaties, which proclamis that Hong Kong blongs to the brits FOREVER, among other things.
Here's a long vid of interview in Chinese: 《鲜为人知的1982年香港回归中英谈判内幕: 中英谈判（1）:邓小平抱怨 “没法和这个女人谈”》 Source