Has anyone considered creating scenarios for this? It would not be hard to add rules for terrain either.
Imagine, scenarios (with terrain) for Bull Run, Gettysburg, Missionary Ridge, etc.
Terrain rules could be borrowed from the 4th Edition Napoleon: The Waterloo Campaign, 1815. Suggested rules:
Woods: Infantry are normal, Cavalry must stop when entering and not battle that turn, Artillery cannot enter or fire into woods.
Buildings: One Infantry in a sector may occupy one building area and receives one less damage marker that turn (only once per turn). Only infantry may occupy a farm and cavalry may not attack infantry in a farm.
Stream: Limits the number of units crossing to only 2 per battle round to engage or disengage, or one of each. Artillery may fire across.
Hill: Artillery on a hill does one more damage, once per battle round.
Here is a battle map of the First Battle of Bull Run