CCP controls Hong Kong since the return from the British in 1997, the deal is one country two system but CCP been slowly remove any autonomy from HK. There's been protest over the years but nothing this prolonged or violent. I guess Hong Kong people had finally had enough and the extradition law is the last straw.
Most people from Hong Kong say they are from HK and not China, which of course upsets the CCP. But many if not most mainland Chinese especially those in the middle/upper economic class view HK as part of China and should follow the same political rules.