New York has been a "majority minority" city since the mid-80s. Effective law enforcement and high real estate prices seem to be the factor in "keeping the peace" there, to say nothing of the fact that immigrants to NYC typically learn enough ghetto English to function in a multiethnic society.
But to keep the peace in Brazil, they’re implementing a system of race preferences:
http://www.washingtonpost.com/ac2/wp-dyn/A62685-2003Jun15?language=printer
Ethnic doesn’t mean race:
eth·nic [ éthnik ]
adjective
Definition:
1. sharing cultural characteristics: sharing distinctive cultural traits as a group in society