Does the empire have a standing army or is the local nobility responsible for maintaining them on their own?
Historically, the guy in the Big Chair maintained an army barely larger than his nobility. It was up to each noble to police their own territory and contribute troops to the king in times of war. Often the local nobles were expected to go with the king to war. This was simply a matter of insurance. If the locals were with the king, then they would be certain to bring as many of their troops as they could spare for protection. Additionally, they couldn’t be at home to seize power.