These are just a few Ideas off the top of my head. Religion could be used as nation affiliation i.e Union, Confederate and what ever other factions you decide upon. To accurately portray this building like "States Rights" and "Federalism" would be in their respective state to provide a permanent base affiliation so if either faction takes a north/south state they will always have some unrest. Similar to what Sicilian Vespers has done with monasteries. Other building could represent abolitionists in certain states where they were most active. Scripted battles would be great but letting the game play out might be more interesting and player friendly. Using the legion system (im not sure how it exactly works) so units created in a state would have 1st New York, 3rd Virginian and so forth would be cool. Making units regional aside from the regulars. Using the castle settlement to represent important forts such as Fort Wagner. A navigable Mississippi river. I will try and think of more suggestions later after I have had my coffee.