What are the best rules for Army-combat
I have a plot that requires the PC's to chose one of three factions, and twice in the story, there will be major battles between the factions and their respective armies, and these will have been improved, or sabotaged, by the PC's to further their factions gain. One army is mainly just gunslingers and tanks, one is naturistic and animalistic mutant-druids, and one is sorcerers and necromancers, so it has to be compitable with the system for powers, in particular Mutations, sorcery, and magic.
Any ideas?