Thanks for clarifying.

Absolutely agree with last para so I do not think we disagree significantly.

I think it is worth adding that, we also get similar behaviour based on other differences: caste in India does not have such obvious physical markers (not to an outsider anyway) but being low caste in India has a history (longer!) very similar to being black in the US. Ethnic splits in other countries might be based on family name, language, religion,.... any identifier that might be even partially inherited.

Edit, to add: This might be a product of living in different countries and cultures, but there are many cases where I cannot tell what "race" people are from their appearance. Light skinned Indians and black Americans, dark skinned Mediterraneans, Central Asians....