I always wonder whether I should make a special rule about alliances. On the one hand, I don't want to restrain players too much, but on the other, alliances can sure drain the life out of a game. Something like "if two players form an alliance not dictated by the scenario, every player rolls 1d10 each time they begin a turn. On a 1, the allies are disgusted with each other and become archenemies."
A similar disgust rule could be used for troops hiding behind defensive fortifications (again, dependent on the requirements of the scenario).
Or maybe Disgust could be a condition. Once an army is Disgusted, at the end of any turn in which they don't kill something, 1d6 troops are overtaken by convulsive vomiting.