The United States was oppressed before the founding of People's Republic of China (PRC). Why oppress black people?

Americans are immigrants from European countries (that is, poor people who can't get land and jobs). Their oppression is that the rich class oppresses the poor class, but they also admit that they are citizens of all countries (their basic rights and interests are protected by law and morality). But black people are slaves (goods, not people). Europeans protect people, not goods. Oppressing black people to overwork them is as natural as overloading your machine and killing them.

Supplement: At that time, many black people were not captured by white people, but black kings and nobles sold their own people to Europeans as commodities in exchange for' peep shows' and luxury goods, so many black people regarded themselves as commodities and resigned themselves to fate.