I suspect the Roman "war machine" really developed as an accident. The Romans are trying to solve social problems in the fourth century and the reforms had the mostly unintended byproduct of making them really good at war. 🧵1/
I say mostly unintended because most *intentional* attempts to forge a war-like society seldom result in effective war-making. Perhaps the most salient example in the ancient world is Sparta, which had a narrow, self-curated elite militarized in the most bespoke way. 2/
The the Spartans basically suck at war, in no small part because they try too hard to be good at it.

There is simply not that much you can do with only a couple thousand guys, no matter how committed they are to hoplite cosplay. 3/
But the Romans in the fourth century are trying to solve serious social problems, albeit in a pressure cooker of significant external threats: Volscians, Etruscans and Gauls. These threats serve as catalysts to force the patricians to the bargaining table again and again. 4/
The aggregate reforms: admission of plebeians to the consulship, curtailment of debt bondage contracts, land distribution and colonization, empowerment of the concilium plebis, each modest in its own right together reconfigure a citizen body and its relationship to the state.5/
In doing so, they create the latent potential for mass infantry mobilization from a large pool of economically prosperous and politically empowered peasants. 6/
It is only around the 340s that the Roman political class realizes the offensive potential and seeks to exploit and intensify it (the Samnite Wars and Latin annexations). 7/
But even this elite has been reshaped by the concessions: ambitious plebeian candidates running competitive elections are far more bellicose. And patrician politicians now need to up their game. 8/
This is one reason why Rome goes from a non-expansionary state in the fifth century to a relentless conquest state by the late fourth. It is doubtful any single Roman has visions of Italian or Mediterranean empire. But the new system brings a new set of incentives. 9/
The incentives are electoral success. Roman elites act the way they do because they want to win completive elections. 9A/
As the elites discover, to their pleasant surprise, that those political and economic concessions allow them to tap a new manpower pool; they prove willing to make new concessions to maintain access (nexum abolition in 326; provocatio in 300, the lex Hortensia in 287). 10/
All worth making for ambitious aristocrats who suddenly have hopes of commanding a two-legion consular army for one ultraviolent year 11/
By the time militarization is more of a conscious policy in the late 4th century, it is now mediated by the popular mechanisms (tribunes, assemblies): for example the people achieve the right to elect 24 military tribunes for the consular legions and duoviri navales in 311. 12/
The Roman army remains a citizen militia, manned by once and future voters and led by elected magistrates and officers. These features are maintained even as the army scaled up from a small urban muster of perhaps 3000 troops in the fifth century to a hegemonic force. 13/
Cards on the table: this thread is un-reformed Millarism. Rome democratized from the fifth to the early third century, as a means of maintaining civic peace. In doing so it created essential conditions for mass mobilization and aggressive hegemony during the Middle Republic. 14/
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