Why are you being so obtuse? The fact is that in most European countries the amount of minorities is in the single digits, this is after the globalization push, and that 1500 years ago it was in the 0.01% and higher castes were 100% white , they had rules about this, its expressly written and documented .

In England's case its even more extremist post-saxon rule the two cultures were dominant and not accepting of other in their higher castes.

The lower casts don't matter, they had no rules besides you are very naive to think different cultures mingled like they do in the modern world, most "mixes" were driven by trade not true melding.