As far as on how "White Supremacy" started; I don't think it is an sole US problem.
All of it already started by the Catholic church during the "crusader" time ; murder everyone who's not catholic or "white". Plenty of examples: Murder all the Inca's, Aztecs etc. and convert them of what is left; that is why S. America speaks Spanish and is predominantly Catholic. Here in N. America "all the unwanted religions" in Europe were sent here. Mostly "white religious" people, like Mormons etc.; the same happened; murdering all the Indians stole their land as well pushed Christian religion. Indians who were left were not good workers for the fields; thus import slaves and go bravely to church and murder slaves, if they objected to their treatment. In the Netherlands they have the Spanish Santa Klaus (with X-Mas) with "black" servants (slaves) as was custom in Europe in those days; which means the Spanish (Later French) Catholic church is really the culprit and cause of "White Supremacy". Religion plays an big role in our present dilemma. Even our present President as well Pence hates everything which is not white or "Christian".
That is how it started even at 1000 AD.