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You really, really have your data wrong. Obviously you have a cliché-type idea of what Mexico it's. http://www.sciencemag.org/news/2014/06/people-mexico-show-st...

The diversity depends on people’s own attitudes towards it, and their sense of national identity.

For example there are some ethnic minorities in Japan but the government has long been against that in order to preserve a unified national identity.

Is there a strong national identity or fragmented identities and loyalties?

Russians aren't homogeneous though?

Russians are but they are only ~80% of the population of Russia.

I don't think you can pin all the crime on "individuals of Caucasian nationality" and Tatars

I don't think so either but there are quite a few degrees between "all the crime" and "zero crime".