Rome’s was a surprising example of successful ethnic assimilation, Randall Collins suggests:
After about 60 BC, most of the famous authors and politicians had been born outside of Rome: Cicero, Catullus, Virgil, Horace, Livy, and Ovid all came from remote parts of Italy. During the following centuries of the Roman Empire, virtually none of the famous names were born at Rome, and they came not only from Italy but from the provinces. At least in the wealthy and educated classes — the only people that we hear about in the histories — ethnic distinctions had disappeared. Latin became the universal language throughout the western provinces; all traces of local cultural identities disappeared. In the eastern part of the Empire, where the provinces had been under Greek-speaking rulers, Greek continued to be spoken but Latin was used in official matters. With the end of a few areas of die-hard resistance, one hears no more of ethnic nationalist movements. The upper classes and the upwardly mobile, at any rate, lived their lives as Romans.
And They All Lived Happily Ever After?
Well, not exactly. The rich kept on getting richer, the poor more displaced from anything except seeking handouts. Generals became politicians and vice versa. Although the ethnic citizenship issue was settled, the struggles turned into civil wars over personal power, until domestic peace was finally established by a hereditary monarchy.