Thanks for the information about racial referents used outside of the USA.

I think that African Americans use that catch-all referent because most of us don't know which nation or nations our African ancestors came from.

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If I didn't say it before, I think the main reason why the term Afro-American didn't succeed in being the formal referent for Black Americans {from the USA} is because "Afro" doesn't refer to a geographical place {like German, Irish, Italian etc} does.

But also "Afro" is the name of a hair style.
And who wants to have a formal group referent that is the name of a hair style?

Not me.