In Medieval Empires, player has both Active Army (used for battles) and Army-Setups (used for pre-setup for quick army assemply). Both numbers are determined by the Level of the Military Headquarter. However, the number Army-Setups is different from the number of Active Armies even for the same level of Military HQ.
In the table below, you can see the configuration of armies with different HQ levels.

#Armies = Amount of Armies the player can control by the HQ (Active armies, not Army-Setups)

SizeArmy = Maximum size of each army (including leader)

CoOp-Army = Maximum size of a cooperative army, where players do a combined attack

Max Units per type = Maximum amount of units a player can own until production of new ones for this type is locked