I don't like how there are sometimes cases where I can't join a battle. For example, when an enemy vassal is in battle with a bandit party, I can't join because both sides are hostile. If I recall, Warband allowed you to pick a side to join at least under some circumstances(or at least in some mods, I can't remember). After the battle, you would still be hortile unless your relation became positive with the faction you joined, You would be temporary allies with the side you chose and it could be used to gain relation or simply as an alternative of waiting the battle out. Obviously, this concept of enemies just allowing you to temporarily join forces with them and trusting you not to take advantage of the situation is not entirely realistic... but this is Bannerlord, where you can make great friends with people by defeating them in battle again and again. lol Realism is not first priority for me here.

Three sided battles would be even more fun, but probably way harder or more tedious to implement.