Hong Kong Basic Law Article 23 (Chinese: 香港基本法第二十三條) is an article in the Basic Law of Hong Kong. It states that the Hong Kong Special Administrative Region “shall enact laws on its own to prohibit any act of treason, secession, sedition, subversion against the Central People’s Government, or theft of state secrets, to prohibit foreign political organizations or bodies from conducting political activities in the Region, and to prohibit political organizations or bodies of the Region from establishing ties with foreign political organizations or bodies.”
Hongkong didn’t enact it for 23 years and CCP felt HongKong is against mainland China more and more heavily. This is why CCP finally decided to propose it.
One country two systems was a product of compromise. Now both sides forgot how to compromise and lost patience.