What actually happens is that an area becomes predominantly occupied by a particular ethnic group. They bring with them their own culture and mementos of home, their own shops, their own clothing, their own food, their own language etc etc.
It has nothing to do with integration or that mythical and spectacular failure 'multi-culturalism'.
Welcoming encouragement suggests that they feel afraid to be here and are tentative in mixing. Far from it, they mix with each other, and when all neighbours are the same it's not difficult. Why integrate (whatever that is) when you are the ethnic majority. And we couldn't see this coming ?? Staggering.