From publisher blurb:
Master the Art of Warfare!
The mass combat rules presented in Pathfinder Roleplaying Game: Ultimate Campaign allow players to take their conflicts to a new order of magnitude, allowing them to command entire armies. While useful on their own, these rules present several new elements that are ripe for expansion. As every general knows, many different aspects of a battle can decide its outcome, from tactics and commanders to the layout of the battlefield and the equipment issued to the troops.
This book provides a variety of additional options to build upon the rules presented in Pathfinder Roleplaying Game: Ultimate Campaign. Make the battlefield truly treacherous by placing it in a lightning storm or wild magic zone. Outmaneuver your foes with new army tactics like a cavalry brace or siege bombardment. Lead your army in style with new commander boons like mad dog and mastermind, and outfit your troops with the best in new resources, such as boats, potions, and repair supplies.