There is a new book getting quite a bit of press coverage: The Big Sort. The very basic premise is that people are increasingly choosing to live near people with similar political and social views. The book is largely about the social and political implications of this phenomenon and I leave it to those experts to comment on this, but the economic undercurrent is interesting to me.
Modern economic organization has made us a country of drifters. We think nothing of applying for jobs across the country, or to move to where we want with some confidence of making a living. Part of this happens because we generally have had a very low unemployment rate so there is a lot of truth behind the belief that jobs can be found most places (at least in bigger cities). Part of this happens because it is so easy to do so. Improved information technology it is easier for firms to recruit across the country (and now the world - imagine the big sort on a international scale...) and for job seekers to find jobs across the country. Highly liquid credit markets make moving much less burdensome than in many other countries. With strong tax incentives to own homes, development of new homes and communities is very rapid, allowing for easier sorting.
So it may be that sorting is happening and threatens the fabric of our society, I don't know. What I am pretty sure of is that this is yet another phenomenon that could not have happened without the economic development and economic system we have developed in the late 20th and early 21st century. So it does not surprise me that this is a very recent phenomenon.