[sahmeepee]

An argument can also be made for a similar effect on language. In the UK in recent decades I've noticed a trend towards young people from various regions adopting a specific south London accent or dialect. Ironically although this seems to be part of adopting the culture of south London, it is also abandoning the dialect of their region which traditionally in the UK has been a very powerful source of identity.

In the town in England where I grew up I could easily tell if someone was from the nearest town (<10 miles away) within a few sentences, or the city a similar distance in the opposite direction. I suspect that won't be possible once the current generations have died out.

Homogeneity is just a natural result of more effective mixing.