the Roman empire got by for hundreds of years with a diverse ethnic make upno ethnic solidarity= no peoplehood = no country. This is how life works, since time immemorial.
America is nothing but a land mass for international commerce and gentile labor. Social solidarity? LOL forget it.
Expect numbers to skyrocket. We all hate each other. Nobody is going to "sacrifice for the common good." There is no common good anymore.
and it wasn't ethnic strife that killed it off either