So, what can you do with this idea to provide more things for players to do, while not making it overall harder to fight wars? Say, provide ways for other players to get involved? What bonuses can you provide to offset any penalties that you propose?
Here's one way to do it:
1. Soldiers no longer automatically consume food from regions they go through.
2. Units have a new stat: provisions, which uses exactly the same mechanic as equipment damage.
2a. When provision>0, units consume x provision per day. This should be made so that each unit can last roughly y days on the field (roughly 7?) with some variation. Cavalry would consume more, and there may be regional factors.
2b. To replenish your provisions, you must buy food from a region with a marketplace or a player who has brought a caravan.
2c. When you run out of provision, your unit start dieing and deserting with the exact same mechanic as currently applies.
3. The caravan mechanics is otherwise completely unchanged, and food from caravans can be used when provisions are depleted. Soldiers with caravans can have brought extra food with them. Traders can steal food on the black market. Soldiers with caravans can loot food and take it from the region, and then sell it to other players who need it.
This wouldn't make war so much more difficult. This would make marketplaces in your own realm more important as the soldiers would need them instead of just picking up food as to go around - in most places there is one in the capital, and you should need it roughly each time you refit.
For very long expeditions, it would would require to either loot the territory they are passing through or go in convoy with extra caravans.
Selling directly to soldiers may be restricted to traders, but ordinary soldiers should be able to get food directly into their caravans by looting. Therefore traders would only really be required if you want to travel a very long way without looting. That makes sense.
It would also give a better sense of a supply line than the current "we just walk there".
