Most empires have been diverse, not homogeneous. Empires attract people from surrounding areas and / or empires absorb people, ideas, culture, from other areas. Ever heard of the term "brain drain"? It's diversity that empires benefit from to the detriment of other nations.

I'm curious: when did America lose it's homogeneity to you? Was it when the Dutch joined the English in New England? Was it when Africans were brought in chains to America to work for free without enjoying the benefits of citizenship (or even acknowledgement of basic human rights), generation after generation? Was it when Irish, Italian and Polish Catholics joined the European protestants in America? Was that when the instability of the family and homelessness started? Was it when Chinese and Japanese immigrants joined European immigrants in the 19th century? 

Or does diversity only mean different skin colors today? Did diversity start when YOU noticed immigration? YOU are a part of diversity you hate.