I really strongly disagree with the sentiment of this comment. I've been living and working in a very ethnically / culturally diverse non-profit charity organisation for several years now. We're a Christian charity, so there are strong religious ties across the board, but huge cultural differences.
A sense of community is far more developed by the shared experiences together, rather than just the similarity of past culture. I always had a very strong sense of community with the people I did my initial training with, and the people I worked with every day. Much less so with the people from a similar culture.
I'm currently living in Carlisle, in the North of England. Very mono-cultural, very white, working class, etc. There's really not a lot of sense of community at all. After the flooding a few years (shared experiences) there was. But here now? No. Most people just sit at home in the evenings watching TV, and never do things together (much shared past / culture, they often watch the same shows, but no shared experiences, so little sense of community).
My wife and I work quite hard to deliberately develop community, inviting people over for meals, (board-)games evenings, barbecues, etc.
But the thing is now, you have to be deliberate about creating community. It's no longer automatic.
Personally, I blame TV hugely. It's far too easy these days to spend all ones free / down time disconnected from the people around you. The internet just continues the trend.
In our organisation, on board our ship(s) ( http://www.logoshope.org/ ) which doesn't have TV, when people started having their own laptops that were able to watch TV series and movies on, we saw a huge shift in community, from people in free time hanging out together and talking, playing games, exploring, etc, to people sitting on their own in their cabins playing computer games, watching TV / movies, etc. And the sense of community suffered.