Mono-cultural areas are areas where nobody wants to move to. These are almost exclusively third-world countries.
The borders of nations are a bad separation or aggregation for cultures, we'd have to look at cultures by themselves and compare results there. But for now the immigrant percentage of the population has to do:
https://en.wikipedia.org/wiki/List_of_countries_by_immigrant...
China, Indonesia, Vietnam, Madagascar, Cuba, Lesotho, Philippines, Burma, Morocco, North Korea, Somalia, Eritrea, Colombia, Afghanistan, ...
That's where you can find regions with pristine mono-cultures.
Comparing these to truly multi-cultural countries like Switzerland, Hong-Kong and Australia I strongly doubt your hypothesis.
The borders of nations are a bad separation or aggregation for cultures, we'd have to look at cultures by themselves and compare results there. But for now the immigrant percentage of the population has to do: https://en.wikipedia.org/wiki/List_of_countries_by_immigrant...
China, Indonesia, Vietnam, Madagascar, Cuba, Lesotho, Philippines, Burma, Morocco, North Korea, Somalia, Eritrea, Colombia, Afghanistan, ... That's where you can find regions with pristine mono-cultures.
Comparing these to truly multi-cultural countries like Switzerland, Hong-Kong and Australia I strongly doubt your hypothesis.