The Social War coincided with the beginning of Rome’s wars with Mithridates VI of Pontus – the last real competitor Rome had in the Mediterranean world, whose defeat and death in 63 BC marked the end of the last large state resisting Rome and the last real presence of any anti-Roman power on the Mediterranean littoral. Rome was not out of enemies, of course, but Rome’s wars in the decades that followed were either civil wars (the in-fighting between Rome’s aristocrats spiraling into civil war beginning in 87 and ending in 31) or wars of conquest by Rome against substantially weaker powers, like Caesar’s conquests in Gaul.

Mithridates’ effort against the Romans, begun in 89 relied on the assumption that the chaos of the Social War would make it possible for Mithridates to absorb Roman territory (in particular the province of Asia, which corresponds to modern western Turkey) and eventually rival Rome itself (or whatever post-Social War Italic power replaced it). That plan collapsed precisely because Rome moved so quickly to offer citizenship to their disgruntled socii; it is not hard to imagine a more stubborn Rome perhaps still winning the Social War, but at such cost that it would have had few soldiers left to send East. As it was, by 87, Mithridates was effectively doomed, poised to be assailed by one Roman army after another until his kingdom was chipped away and exhausted by Rome’s far greater resources. It was only because of Rome’s continuing domestic political dysfunction (which to be clear had been going on since at least 133 and was not a product of the expansion of citizenship) that Mithridates lasted as long as he did.

More than that, Rome’s success in this period is clearly and directly attributable to the Roman willingness to bring a wildly diverse range of Italic peoples, covering at least three religious systems, five languages and around two dozen different ethnic or tribal identities and forge that into a single cohesive military force and eventually into a single identity and citizen body. Rome’s ability to effectively manage and lead an extremely diverse coalition provided it with the resources that made the Roman Empire possible. And we should be clear here: Rome granted citizenship to the allies first; cultural assimilation only came afterwards.

Rome’s achievement in this regard stands in stark contrast to the failure of Rome’s rivals to effectively do the same. Carthage was quite good at employing large numbers of battle-hardened Iberian and Gallic mercenaries, but the speed with which Carthage’s subject states in North Africa (most notably its client kingdom, Numidia) jumped ship and joined the Romans at the first real opportunity speaks to a failure to achieve the same level of buy-in. Hannibal spent a decade and a half trying to incite a widespread revolt among Rome’s Italian allies and largely failed; the Romans managed a far more consequential revolt in Carthage’s North African territory in a single year.

And yet Carthage did still far better than Rome’s Hellenistic rivals in the East. As Taylor (op. cit.) documents, despite the vast wealth and population of the Ptolemaic and Seleucid states, they were never able to mobilize men on the scale that Rome did and whereas Rome’s allies stuck by them when the going got tough, the non-Macedonian subjects of the Ptolemies and Seleucids always had at least one eye on the door. Still worse were the Antigonids, whose core territory was larger and probably somewhat more populous than the ager Romanus (that is, the territory directly controlled by Rome), but who, despite decades of acting as the hegemon of Greece, were singularly incapable of directing the Greeks or drawing any sort of military resources or investment from them. Lest we attribute this to fractious Greeks, it seems worth noting that the Latin speaking Romans were far better at getting their Greeks (in Southern Italy and Campania) to furnish troops, ships and supplies than the Greek speaking (though ethnically Macedonian) Antigonids ever were.

In short, the Roman Republic, with its integrated communities of socii and relatively welcoming and expansionist citizenship regime (and yes, the word “relatively” there carries a lot of weight) had faced down a collection of imperial powers bent on maintaining the culture and ethnic homogeneity of their ruling class. Far from being a weakness, Rome’s opportunistic embrace of diversity had given it a decisive edge; diversity turned out to be the Romans’ “killer app”. And I should note it was not merely the Roman use of the allies as “warm bodies” or “cannon fodder” – the Romans relied on those allied communities to provide leadership (both junior officers of their own units, but also after citizenship was granted, leadership at Rome too; Gaius Marius, Cicero and Gnaeus Pompey were all from communities of former socii) and technical expertise (the Roman navy, for instance, seems to have relied quite heavily on the experienced mariners of the Greek communities in Southern Italy).

Like the famous Appian Way, Rome’s road to empire had run through not merely Romans, but Latins, Oscan-speaking Campanians, upland Samnites, Messapic-speaking Apulians and coastal Greeks. The Romans had not intended to forge a pan-Italic super-identity or to spread the Latin language or Roman culture to anyone; they had intended to set up systems to get the resources and manpower to win wars. And win wars they did. Diversity had won Rome an empire. And as we’ll see, diversity was how they would keep it.

Bret Devereaux, “Collections: The Queen’s Latin or Who Were the Romans, Part II: Citizens and Allies”, A Collection of Unmitigated Pedantry, 2021-06-25.