The U.S. is a melting pot. The various groups that entered are obviously not under the banner of "US" since arguably, they didn't hate themselves.
What you're saying is that an elitism was in place that targeted each next immigrant population.
Also, there were always some persons who had open arms to the immigrant, and others who lived in fear of other.
Essentially, it's the old Anglo-Saxons who set up the cultural pyramid. Any group seeking to assimilate had to find, carve out, and develop its own niche.
Similar ethnic divisions exist in many other regions, and have been exacerbated by European colonial elites. Just look at Africa's recent history.