There is interesting CIA report on this -
The CCP's plan was to use potential military take over of Hong Kong/ Macau as a backup plan in the event of USA triumph over CCP as they believed this would legitimize CCP among Chinese citizens in event of humiliation from USA.
They gave plan a try during Suez crisis by threating UK they would take over hong kong
The British already humiliated in the Suez crisis were in no mood of hearing from creatures they consider opium guzzling filth. UK responded with a threat of turning opium guzzlers radioactive
UK pondered China nuclear attack
Like a typical naking cuck, Mao gave a submissive blush and dared not even to look at Hong Kong even when China had developed ICBMs in range of covering UK
You have missed
Austo- Hungarians
https://en.wikipedia.org/wiki/Austro-Hungarian_concession_of_Tianjin
Belgians
https://en.wikipedia.org/wiki/Belgian_concession_of_Tianjin
French
https://en.wikipedia.org/wiki/Shanghai_French_Concession
German
MORE THAN JUST KIAOCHOW BAY: A (NEARLY) FORGOTTEN STORY
Italians
https://en.wikipedia.org/wiki/Italian_concession_of_Tianjin
Russians
https://en.wikipedia.org/wiki/Amur_Annexation
China was the proverbial colonial village bicycle, almost every colonial/imperial power had the satisfaction of riding it