You can simulate history in many ways.
“armies are recruited from pops; each regiment in your army is directly tied back to the pop that supports and reinforces it. If the pop is radicalized, so is the unit. If the pop is depleted by losses (or job changes, emigration, etc.) the unit stops reinforcing.”
https://acoup.blog/2021/08/13/collections-teaching-paradox-victoria-ii-part-i-mechanics-and-gears/