Stealing some ideas from other games:
- NM loss even if you "win" a battle. The old SSI game No Greater Glory had this. If the North had Antietam and Shiloh the same week, the population would have been horrified by the losses, even with the tactical victories. In that game, if you had too many battles at once, you could lose support even if you won all of them, due to the mass casualties.
- Filling high level bureaucratic positions, like war, navy, economic ministers. Like No Greater Glory, Hearts of Iron, and probably a dozen other games. There were real, and significant, controversies, brilliance, and incompetence at those higher levels that had measurable impacts on the outcome of the war.
- Trading $ for better weaponry. I think it was Grant Lee Sherman/Civil War 2, the game with all the tactical battles, that allowed you to do this. You could "buy" Henry rifles for everyone, but it cost a fortune to resupply ammunition. Also related to a real life controversy that happened in the war department in the early days of the war.
- Ability to promote all your generals, regardless of history. Like every other game. I'd be cool with limiting it to only when you choose "randomized generals," since that would conceivable also randomize their ability to be promoted.
- Generals picking up special attributes, like the Total War games. Attack a fort successfully three times, get that ability. Lose 4 battles in a row, get that negative attribute. Sit still in a city for three years, lose the fast mover trait, get a recruiting trait. Etc.