"white" is a concept made up to justify slavery and white supremacy. you are actually hitting on something really important, the definition of being white HAS varied widely in history. when the concept of whiteness was first being developed, it was in order to justify categorizing people as white or non-white, and then the eugenics movement ran away with that concept to promote racial supremacy- not racial identity, but racial supremacy. so "white" as a category did indeed refer to specifically condoned peoples with supposed genetic, moral, intellectual superiority. and the definition of "white" did indeed vary then as well as now. irish, italian, slav, spanish, jews were all once distinctly non-white by the definition of "whites" at one point. the definition has changed since then because it has always been a non-scientific concept designed to identify "us" from "them" and justify the subjugation of whoever was considered non-white at the time.