I think the equivalent of various native tribes would be Romans, Etruscans, Samnites, Greeks etc. The core "Italian" Romans were themselves a mix of various Italian populations and they even fought the social wars to gain equal rights. And outside of that we have the Celt, Iberians, Berbers, Mainland Greeks, Anatolians, Illyrians, etc.
Broadly speaking you cannot draw an equivalence between Roman Empire and Americas because the dominant ethnicities in US, Canada, Brazil, Mexico and other countries are from outside. But IMO this would be the closest analogy.
The equivalent would be if the Italian Greeks had become the dominant ethnicity in Italy and absorbed the Romans, Samnites, Etruscans, etc into their culture.
Broadly speaking you cannot draw an equivalence between Roman Empire and Americas because the dominant ethnicities in US, Canada, Brazil, Mexico and other countries are from outside. But IMO this would be the closest analogy.
The equivalent would be if the Italian Greeks had become the dominant ethnicity in Italy and absorbed the Romans, Samnites, Etruscans, etc into their culture.