They could also add factions from Europe like:The German Empire, France, Great Britain, Hasburg Empire, Spain, Mexico, countries that had a slight effect on America for trade, and then have US factions like: Army of Northern Virginia (Lee), Army of the Potomac (Grant), Army of Tennessee (Hooker), with other generals of the Civil War packed into those armies. Also, the campaign could start a little before the South seceded from the North in a period where as the Union (at the time would just be the US) you could be dealing with unrest in the south, and as the "Confederates" (also still US but a separate faction) you could be building up your armies and dealing with the Mexican armies for control of Texas. Not sure if this would work too well but it's an idea that I would love to see!