I really dont like any type of artificail pathblocking, but everything would be better than current state of affairs). In some cases I can imagine, that the only available road for troops goes through enemy castle (mountain passage, river cross) but historically castles were much more than just a checkpoint.
From my point, castles are not only some kind of a barricade, but also a military backbone of the kingdom, a shelter for locals and a storage in cases of war. So:
1) Top tier troops recruiting and upgrade should be only in castles, whilst mid- and low tier in villages/towns.
2) Local villagers should look for shelter in nearby castle, when they detect upcoming enemy armies, and leave theit huts with all the possesions and cattle. As a result, huge armies have little to none chance to surprise cunny peasants at their beds, but small dedicated foragering parties wiil do the trick (maybe under one of your companions command). And of course those refugees can give some temporary boost to castles garrisons and foodstocks. So, enemy parties can rest in abandoned villages, but not loot them.
From this point there could be even a special policy for a kingtom at war to force their peasants to stock food mostly in castles. For example it will give a huge economical nerf, but make enemy parties starve on your territory.
3) Yeah, starving armies. There're none in the game right now, cause your can take enormous amount of forever fresh food. But we want our rotten chicken right now!
4) It would be great, if castles could sent mobile patrols to defend villages from bandits and raiders or even intercept small warparties, if they are confident enough to defeat them. There's a mod out there which lets you to hire patrols, the thing is to implement this idea in a more consistent way.
All this foraging mechanics could be adjusted due to cultural references of war parties and troop types. For example, nomads dont need piles of fodder for horses and have better basic raiding abilities, while other cultures may need some special marauders/scouts for the matter.
The point here is not to FORCE player and AI to take enemy settlements one by one in strict order. But if they choose a distant one far behind enemy lines, they should be ready to eat their horses.
