Making it somewhat risky to completely drain a settlement's garrison, even in the safe interior. I already played around with Captain Oct's fix for it, where the AI focused on closest settlements, and you could cheese the AI pretty hard by jam-packing a frontline castle with about 300 garrison + militia, while running your interior holdings with minimal (or no) garrisons.
That is just the thing, it shouldn't be risky to keep the more interior garrisons running on minimal strength because it is stupid to send a massive army deep into enemy territory like how it is done in Bannerlord. The only troops that should ever be garrisoned in the interiors would be just enough to deal with raids, enforcement and protecting the lord. Basically a police force anything beyond that the value to cost ratio starts dropping off rapidly.
IRL a bunch of border castles wouldn't stop an army 12,000 to 20,000 strong from prancing across the countryside for months on end. People just don't like the way it looks or plays out in Bannerlord.
In open battle sure but there are much better ways to go about stopping a force that is significantly more powerful then yourself.
First off armies don't/can't go carrying around a year plus of supplies while they are marching like in Bannerlord.
- It slows them down and limits travel routes as you can only travel through places that will allow it. With each additional supply wagon slowing you down more then the first.
- If you are bested on the field of battle all of those supplies are now your enemies so the more supplies you send with the army the greater the loss.
- More supplies makes for a bigger target to raid and also makes it much easier to destroy larger amounts.
- Food does eventually go bad so you only carry around enough to feed your men for so long.
- Larger food stores attracts more rodents which carry diseases.
- It takes time to make and gather up supplies which you generally didn't have a very large stock pile of.
So instead you create a supply line so that you are constantly getting supplies in to replace those that were used. You only had 2 methods of transportation land and sea. Eventually though it will come by land which has it's own problems.
- Far easier to attack the supply line then the army itself and hungry soldiers aren't as effective as fed soldiers.
- It doesn't take a very large force to cause havoc raiding your supply lines which means you can kill off an army by starving it with very few men.
- The larger the army the more supplies it needs which makes it harder to live off the land for extended periods of time making them more reliant on those supply lines.
- It takes far more men to deal with an issue then it does to eliminate it before it becomes an issue.
- Due to the amount of time it takes for messages to travel to a location you had to be preemptive with emergency requests since more often then not it would have be too late.
For these and other reasons not mentioned realistically you wouldn't see that tactic working very well long term anywhere in history before the airplane. It isn't just about taking a city it is also about how do you hold and supply it. How do you continue to supply your army as it moves on, how do you protect your supply chain as you get deeper and deeper into enemy territory. How do you protect your army's back so that you don't get caught in between two or more enemy armies.
Many military campaigns ended simply due to the fact that they could not maintain proper supply chains. The only way for 12,000 - 20,000 to prance around in enemy territory for months on end is if they split up into many smaller forces that could survive off the land and what supplies they got from raiding like common bandits. Which is already what the AI does naturally and look how well it works in the game.
To actually represent how it would work in real life armies would only be running around with 1 week worth of food. They would have to have caravans running between friendly cities and the army to supply more food. Guess what would be the most efficient way to deal with armies then. That's right raid those caravans or just prevent any of them from reaching the army so they eventually starve. You only need like 40-50 troops to accomplish that and you could take out an army of 1,000+ in the game then.