One of the things that can be looked at is how Hero's and Generals do a dynamic campaign map, clearly you would have to start officers at a lower rank otherwise there will be millions of troops fighting.
I could see a map of the US with points those points would be tied to different battle maps. Every "player" would start with just 1 division as you win battles and play you will rank up to control larger armies. When you log out your "officers" would control the divisions in battle. Once 1 side wins you reset the map again every one starts over. It has worked fairly well from what I saw in that game even though that is primarily a FPS if there is enough points you might have smaller battles then every battle being Gettysburg or Fredrickburg.
It would encourage players to work together, and plan there attacks and menuvering on the map as 1 division against 10 even if the AI is controlling the 10 has no chance to win like in real life