Ever spent any time in Houston, Los Angeles, Miami, San Jose, Casper, Traverse City, Nashville, New York, Buffalo, New Orleans, Cortez, Lubbock, Chicago, Salt Lake City, Minneapolis, Jackson, Boston, Seattle?

In your mind, are these all filled with people who look the same, sound the same, practice the same religion, immigrated from the same place?

Instead of just relying on your intuition, you can just look this up, because it's a well-studied question. One simple search is for "fractionalization". If you'd like me to save you the trouble, then, with respect to your claim here: no.