This is completely wrong. We do not know much facts about the very early Rome, this is earlier than the Punic Wars. But also the little we know is that the citizenship even in these early times was not bent on Latins (which means people of Latium). In the early times, we have a minimum of 3 ethnic groups: Latins, Sabins and Tuscians, and especially the last two were highly represented among the leading families. In any later time, it was very easy to become roman citizen: serve in auxiliar troops or work for your family/city so that it is granted roman citizenship. So every family had the option to gain citizenship within 2 generations. Ofcourse, this was not strictly formalized in the first place, so it was full formalized in the early principate (30 B.C.). The same for former slaves: freedmen had not exactly the same status as freeborns, but their sons had and could even enter Senate.
We can see this in the examples of the dynasties ruling the empire. Traian and Hadrian were from Hispanic origins, the Severi dynasty came from Leptis Magna (today Libya) with punic roots, many of the so called soldier emperors of the third century came from the Balkans/Illyricum.
Plus, the term "barbarian" is greek. It does not fit on everyone outside the empire. For example the Persians were not considered barbarians.
You may argue, this point of view might be supported by vergil's "Aeneis", but this poem is strictly bound on Augustus ruling concept. There is no indication, Romans accepted it as their mission "to incorporate lesser cultures under banner of civilization." It is quite simple: This point of view of the Roman Empire is heavily influenced by the European ideas of the 19th century, especially nationalism and imperialism. Both were not Roman concepts. it is obvious that young nations like, for example, Italy wanted to look on Old Rome in a way they could legitimate themselves by constructing they are fulfilling the Roman legacy, especially if they could argue they are a reborn Rome. But this does not match Roman way of thinking. Romans were usually really pragmatic, so they did not try to conquer regions that were costly to take&control and relatively poor in an economic sense. For example, conquest of Ireland should have been something, Rome was able to do for centuries. They did not to it and they did not even try. Why should they go there, in this poor, far country? But given a motiavtion "incorporating all the lesser cultures under the banner of civilization", Romans would have tried and conquered Ireland for sure.
It was not until the
Social War that the Italians gained full citizenship, and not until ~40 BCE that the Cisalpine Gauls got full citizenship. What you are talking about fits best as Provinciales, Peregrini, or, at best, Socii, who had to fight for their right to citizenship and it only covered Italy. Roman governance reached across the whole Mediterranean, of which the entirety of Spain, North Africa (outside of Egypt), Spain, Gaul/France, Britain, Germany, and Eastern Europe could be indisputably called barbarians. The places of debate would be Greece (Romans pillaged Greek cities and temples, and often distrusted Greeks even though they admired the culture), Egyptians (who the Romans had deep respect for), Jews (who the Romans absolutely did not get along with), and Persians (traditional enemies of Rome). If they were not barbarians, they were likely enemies of Rome anyways. Stating that the word "Barbarian" has a Greek origin is entirely pointless, as the concept reached far beyond Greek borders and existed across Eurasia between Italy and Japan. Even the Colonial Era had the same idea in the word "Savage".
Of these barbarians and enemies of Rome, very few would see full Roman citizenship. Foederati, often Celts and Germans, would offer military service in exchange for
partial citizenship, making them second-class citizens in essence. The Sabines were killed in Roman genocides, and frequently came into violent conflict with the Romans. This gets even worse when you realize that the Samnites were a branch of Sabines, and the Samnites were hit very hard by Roman wars. The Etruscans, who you have dubbed "Tuscians", were the progenitors of Roman culture and, thus, did not suffer as much. However, they still were forced to undergo heavy Latinization that, by the Imperial era, they were almost extinct as a distinct ethnicity.
Again, those who fought for Rome were only granted partial citizenship, not full citizenship.
Rome was founded April 21, 753 BCE. The events you are discussing are actually much later history. It began as a kingdom led by Etruscan kings, with a primarily Latin populace. Then came the Republic. Finally came the empire. The Romans slowly had to adapt themselves once an empire to tolerate the mere existence of other cultures. Even still, frequent cultural conflicts arose between Jews and Romans, Celts and Romans, Africans and Romans, and even Persians and Romans. Nomadic tribes, likewise, had their share of conflict. The idea of Roman civilization was so strong, that it even outlasted the Western Roman Empire. For example, in 526, Cassiodorus wrote of how the Gauls finally became like Romans, instead of Celts:
"Finally you found Roman eloquence in regions that were not originally its own; and there the reading of Cicero rendered you eloquent where once the Gaulish language resounded"
Mind you, "Roman eloquence" refers to the Latin language.
It was not until the
Constitutio Antoniniana in 212 CE/AD that all free people living in the Roman Empire were given full citizenship. The simple existence of non-Italian emperors proves nothing, as the period in question was a period of might-makes-right in which emperors were so frequently killed and replaced, that the Romans invented replaceable parts for statues so they could keep up. Note, however, that all Roman emperors adopted to Roman tradition, and took Latin names, rather than keeping Berber, Aramaic, Illyrian, or otherwise non-Roman names. You may also recognize the granting of citizenship to all people of the Roman Empire as happening about 260 years before the fall of the Western Roman Empire. The math comes out to 1229 years after the founding of Rome, and so if we discount the Byzantine Empire as the Roman Empire (despite it rightfully holding the title without legitimate dispute), then the vast majority of the existence of the Roman Empire, especially while Rome was the capital, occurred in a period where minorities were not given full citizenship, if any citizenship at all.
