Mass Combat Quick Reference
These mass combat rules treat armies as if they were individual creatures. Instead of making 100 attack rolls for each side of a battle between elves and orcs, you treat the elf army as one unit and the orc army as another unit, and they battle each other with just one roll each. Instead of the armies taking turns attacking each other, they roll simultaneously. Smaller armies have fewer individual creatures (units), larger armies have more units, and the number of units directly relates to how dangerous an army is.
Every army has a commander, typically a seasoned veteran, who directs the army's actions. You can lead an army yourself, making you its commander and providing bonuses depending on your kingdom leadership role.
Armies can learn different tactics, such as using reserve archers, forming a defensive wall, or using dirty tricks. An army can use strategies like attacking recklessly and aggressively (much like a creature using the Power Attack feat) or being cautious and defensive (like using Combat Expertise). The army's commander decides the tactics and strategy used in battle.
Conditions on the battlefield affect the process and outcome of the battle. For example, muddy terrain slows walking armies but has no effect on flying armies; night combat hinders human armies but not orc armies.
Resolving the battle consists of three phases in which the commanders decide on tactics, the armies make ranged attacks (if any), and the armies then close to melee range. They then remain in melee until one side flees or is destroyed.
The following summarizes the key rolls you'll make when using mass combat:
Offense Check: d20 + Offense Modifier (OM)
Damage Dealt: Offense check result — the defending army's Defense Value (DV)
Morale Check: d20 + the commander's modifiers + the army's Morale score
Beyond the Kingdom
The mass combat rules often refer to aspects of the kingdom building rules, such as Loyalty checks and a kingdom's Control DC. If you aren't running a kingdom, substitute a Will save for a Loyalty check. Instead of a kingdom's Control DC, use the primary ability DC of a monster with a CR equal to the party's APL (see Monster Statistics By CR, Bestiary 291). For example, if the party's APL is 12, the Will save DC is 21. Instead of a kingdom turn or kingdom phase, use 1 month. Instead of BP, multiply the BP cost by 500 gp.
Running Mass Combats
Since an army's strength is represented by an ACR score, the GM can balance armies against each other using the guidelines for CR. For example, two ACR 9 armies should make for a relatively even battle, but so would an ACR 9 army against three ACR 6 armies. This applies mostly to typical humanoid armies, as monsters with powerful abilities might be significantly more formidable.
Recruiting Armies
If you are a leader of a kingdom, that fact is sufficient for you to recruit armies from your citizens. If you are not the leader of a kingdom, the GM may decide that you need to achieve some sort of in-game accomplishment to earn the respect and renown needed to raise an army.
Being able to recruit a monster army usually requires a special quest or adventure; you can't simply recruit an army of goblins to serve you because you've found a tribe of goblins or know they live in your kingdom.
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