Here's an idea I'm working on and would like to see your thoughts. The map is a basic Europe shell, though I'm adding in cities, because I like to fight for key areas rather than simple land.
I'm playing with the bonuses, only England and Spain are complete to give an Idea of what I'm thinking.
The idea is to simulate a city under siege, so if you can't control the land around your city, it's actually kind of a drag on your country to try and feed and clothe your people, so you get penalized.
I think the game play would also play on this idea of 'supply' by giving you negative armies for each territory you try to hold.
It would need a lot of tweaking to get the right feel, but thoughts?