Created an account just to comment. Pretty fun game! I realize it's not exactly meant to rival EU4 in complexity, but I could see this game getting there with a few thousand hours of dev work XD It has the potential, however far you want to take it. Anyway feedback:
Stalemate wars suck. There doesn't seem to be much you can do to influence them or stop them so once they're going you're stuck. There should be some way to stop a war after X turns, with whichever cities were conquered switching sides. If that means white peace so be it.
Endgame becomes a little trivial if you just wait, With 400 power, you can almost instantly enslave mid sized countries of 4-5 cities. Because dark forces are so powerful after weakning the world via famine, this allowed me to win a game after my initial dark uprising got crushed (I did all that waiting because my initial little shadowed empire wasn't doing so hot). Either limiting how quickly you can thrall/shadow/enslave, or some kind of cap on power (50 maybe?) would take a step to making this less trivial.
Edit: I've actually thought of a potential solution: Thralled characters that are then part of an enslaved city count permanently towards your thrall limit. That way you can't just keep spamming new dark towers once your original ones fall without increasingly higher costs.