Explanation: Rome is somewhat unusual as a massive world empire in that it did not just start as a small city-state, but didn't really stop considering itself as a small city-state even after massive imperial expansion. Arguably, it didn't stop considering its holdings as the extension of the city-state of Rome until the 2nd century AD, or even later!

In its estimation of the world, there was no 'common' pre-existing nationhood that was shared, like the Greeks considered other Greeks to be, in some vague way, Greek; to the Romans, everyone who was not from, or did not perfectly imitate, a single little city in a single corner of Italy was a filthy OUTSIDER! Even if they spoke the same language, like those filthy L*tins! For reference, this is the extent of the Latin language (and thus the Latin people) early in Rome's history (Rome is located inside of the 'Latin' territory)

... however, Romans also would, in the Late Republic and the Empire, also gain a reputation for warring with each other. Damn Romans! They ruined Rome!