Quote Originally Posted by Caravel
Normal and Hard don't give any bonuses. Personally I mostly play the hard difficullty and rarely the expert, because I like to use tactics that rout the enemy units off the field, not butcher them to almost the last man and artificially inflate my own unit's valour.
Actually, the M:TW A.I. does get a small combat bonus on hard, but it is barely noticable. Expert gives a slightly bigger combat bonus as well as +4 morale to the A.I. In R:TW off course the A.I. get a clear combat bonus on hard and an even larger one at very hard.