The simplest way to do that would be to simply say that you can recruit at each city or stronghold and the troops of lesser regions could be recruited at the nearest city or stronghold defined by how many miles away they are.
Not saying it would be SIMPLE mind you. But I think that would be the simplest way to do it.
It could also be done where all regions of a duchy would send their troops to the duchy capital. The main problem I have with that idea is that it would incentivize realms to have only one duchy. We would lose the great multi-duchy realms.
Hence why I suggest it simply be hard coded to the nearest city or stronghold.
And yes...I know...simple in this case is not necessary simple or easy. Just MORE simple.
