During the Second Punic War, and the brief Gallic War immediately preceding it, Rome was able to mobilize about a quarter of a million men between the city and its allies in five field armies, most around 50,000. Assuming an Italian population of ~5 million in the third century BC, this represents 5% of the population bearing arms.
These were militia; they fought with their own weapons, in their own style in the case of the Socii, each city and hill tribe in the confederation was responsible for raising its own levy. This is not a centralized, professional system requiring tons of bureaucratic control.
With that in mind, why were the armies of medieval kingdoms and principalities, often with similar or greater population to the Roman Italian confederation, so tiny in comparison? Is it urbanization? Rates of land ownership? Slavery? Republican constitution? What would it take to make a medieval principality raise the [relative] equivalent of the Roman armies we saw during the mid Republic?
These were militia; they fought with their own weapons, in their own style in the case of the Socii, each city and hill tribe in the confederation was responsible for raising its own levy. This is not a centralized, professional system requiring tons of bureaucratic control.
With that in mind, why were the armies of medieval kingdoms and principalities, often with similar or greater population to the Roman Italian confederation, so tiny in comparison? Is it urbanization? Rates of land ownership? Slavery? Republican constitution? What would it take to make a medieval principality raise the [relative] equivalent of the Roman armies we saw during the mid Republic?