Autarch has created a lens with Domains At War. This finely crafted piece allows you to view mass combat within your game. It is up to you to focus the lens, choosing when to pull back and see the whole of a war campaign and when to zoom into a single battle. The rules of D@W work seamlessly, allowing a group to flow back and forth between both rule sets as the story of the game and their interest demands. If you are looking for a rule set for a d20 game that abstracts mass combat in a fun, simple way, while still providing players influential choices, check out D@W.