I’m interested in who has been consistently allowed to be white throughout history?
Only the Nazi created “Aryan” race that lasted all of twenty years tops.
Race is a social construct. Even when there was white on white racism, they still viewed the other race as white. The idea that there is one white race superior to all other white and nonwhite races was was only consistently held and kept by the Nazis.
Every other white race has at sometime, been considered inferior to another white race. Often wars were fought between white ethnic groups to prove who was top, and then decades later another war but with the loser of the prior war winning the next round. The French-English thousand years of conflict is a prime example of this. As part of the justification for war, there was always an ethnic racism that bolstered with both sides having ethnic slurs and racist beliefs about the other. So what you have, is multiple white ethnic groups all simultaneously thinking they are the best of the bunch. It’s called patriotism, but really that’s just a mask for a core belief that your ethnicity is somehow fundamentally superior.
I know that some thought is saying that racism only flows from “whites” to “nonwhites” but this is not true. This idea then requires that white on white racism is explained by saying “oh, but at the time white group x, was not considered to be white” which is absolute nonsense. This is often used to explain the English-Irish racism or Russian-Polish racism or Greek-Italian racism. Humans can actually look at another human with the same skin colour and think them subhuman, animals. Ethnicity cannot be reduced to skin colour alone. It is the sum of everything we are.