Some suggestions i have.
Hunger and morale for military units so you can't deploy them forever. Morale always been a key factor in any battle, units with a poor morale fight poorly. The further away you're from one of the zones you control the lower your morale is (Like 5-10% morale loss for zone). This would make units defending they homes stronger, as they normally are. Ways to prevent morale could be adding captain units (Frail units that boost morale for they units). And maybe slow wagons with provisions that can be used to feed your units when they're far away from your base?. Would be awesome to have a raiding system where you can steal most the masklings and other enemies just like they do with you.