Why might china have opposed british control over hong kong??

so they dont control hong kong

Because, The cultural and economic differences are widely considered as a primary cause of the conflict between Hong Kong and mainland China.

chinese civil war took place over a long period of time between 1927 and 1950. the war was interrupted when japan invaded china in 1936 and by world war ii. the war was fought between the nationalist government of china, also called the kuomintang (kmt), and the communist party of china (cpc).