Been thinking some about the cruelty of the game. The viking age was a cruel place to live in, so the game should reflect that. Slaves were common in the viking countries and their masters could do anything to them without repercussions. They didn't hesitate to kill defenseless people or women and children either when needed. Of course some were more cruel than others. One way to put this into the game might be that the player can decide how cruel his armies are.
A cruel army affects the moral of opponents, but also makes trading more difficult.
Also, when brining in the fantasy element, a cruel army might be more approached by the giants and evil creatures, while a not so cruel army gets approached by good creatures.