The world's oldest roleplaying game isn't necessarily meant for mass combats, but with a few rules additions, this archetype of fantasy storytelling
Tome of Warfare (Fantasy Grounds) - Dungeon Masters Guild
Mass Combat Rules for D&D Released for Free! - Tribality
Fantasy Archetypes: War Priest for the Savage Worlds RPG – Open
The Black Company Campaign Setting by Robert J. Schwalb and Owen
The world's oldest roleplaying game isn't necessarily meant for mass combats, but with a few rules additions, this archetype of fantasy storytelling
Tools of War: 5E Mass Combat (PDF)
Artificer Specialists (New & Updated) - Experiment and Innovate
Gorgon, A D&D 5e Tale of Stone and Redemption by Matthew David
10 FREE Magic Weapons For Your Game (5e D&D)
Human Army Mass Combat Army List – DMDave Publishing