Despite a barrage of hefty bonuses, loosened and more progressive enlistment requirements, and even the creation of innovative pre-boot camp programs, the U.S. military mostly fell short in efforts to bring more Americans into the services over the past year -- and it's unclear how or when that will change.
the US liberally uses become-a-citizen through service schemes and any number of arming/supporting proxy armies would be analogus to roman federates. the PMCs would even be buccellarii or palatini
funnily enough the giant moneypit in the pentagon shoveling the US' budget to private arms dealers is the one thing the late roman state had a better grasp on, with nearly the entire supply-chain and production of military goods run directly
Well Rome was a planned command economy based on pillaging and slavery