Of 1526 when the first slaves arrived on the soil of America. Or 1714 when the first use of the word “white” was used in South Carolina to deliberately disenfranchise negro voters. In all depends on context when mechanism of white racism is being discussed and built up over time. But you are of course correct into pointing to the historical depth of the issue. The white system built up from continual political opposition through those fighting to control it, not down.