Good comment. They're all white europeans and they're physically separated from each other by geography, which makes this importantly not like the U.S. for example. We can see small examples of this in cities that have longstanding (hundreds of years +) minority populations. It's not like they're mixed together, what always happens is there is a "Jewish Quarter", "Chinatown", etc. More like micro-states within a state.

edit: Maybe people thing "Good comment" was sarcastic? I genuinely meant it was a productive addition to the discussion :-) Also, I'm not just making this up. There's significant scholarship on the question.