Some battalions stays in reserve. How to use them?
Battalions in Reserve
Generals have a limit on how many they command, so you can either promote them to increase this limit, or recruit another general and have them split up the forces from that HQ.
Generals belong to a certain state and will only recruit units from surrounding states. You have to click on the recruit at new general and see if there’s a general for that region. If not recruit a general else promote your existing general.