>>18463948
>but white people calling themselves white for over 400 years is invalid for some unexplained reason
But Europeans haven't been calling themselves "White". That's not an ethnicity for Europeans. Their skin is white, but not their ethnicity. They're German, Italian, Irish, Polish, French etc.
Black refers to a completely new ethnicity. NOT skin color. And "White" cannot YET be an ethnicity because white people in America feel that they're still European.
Do you understand that the descends of African slaves in America do not have a connection to their African roots the same way white Americans have to Europe. The African ethnic identities were deliberately destroyed and lost as a consequence of slavery.
With time they're all mixed and they cannot possibly point to any particular point in Africa where they came from. They do not know their ancestors. They have no connection to the Old World.
You now have a group of people that is distinct both from Africans and from the white Americans that surround them. They then developed their own culture, dialect, cuisine, art, music, religion, etc. which are completely separate from anything in Africa. This is ethnogenesis. "Black" is an ethnonym for this group.
White Americans didn't through this process. Once they no longer feel European, they can start calling themselves something else.