A General can only acquire the rank of 4 if he captures a capital. Generals also increase the limit of battalions allowed in one army. You can only have so many Generals in play at one time, and they cost 3 battalions to buy. Forts - Another UR treat. Push deep into enemy territory , then build a fort to protect yourself.
Forts cost three battalions to buy, and are stationary.
You can however demolish forts and rebuild them at new locations. You are limited to the number of forts that you can have at one time. You can set the difficulty level of the rebels when you set up the UR game. Rebels that you capture become battalions under your control. Rebel Generals are just executed, though.