I dislike auto popping angry peasants from entering a region. You can literally just walk across your enemy region without looting and devastate those regions automatically. Don't even need to loot.
instead of angry peasants as a combat unit fighting them have angry peasants slow unit travel - This will make defenders who are already advantageous even better at defending. Remember, BM is a game where defenders already have an easy time defending. Not sure making it even more difficult want people to fight more often.
reduce unit morale - It is already annoying enough to fight outside of your own realm. I am against this idea. If this gets implemented, looting should increase your morale in return.
maybe even steal supplies - This implies that peasants are even allowed to be near any army. Have you ever approached an army base before?
