Yeah, they get them from freed prisoners of a defeated party. They may sometimes recruit them from thier own prisoners too if they're out and about long enough.
The stories some of those imperial peasants could tell... captured by a Kuzait lord... who was then captured by bandits... who they signed up with... who were then captured by a Sturgian lord.... who was then captured by forest bandits... who they then signed up with... only to be mercilessly slaughtered by some human player.