In the lore/intro there is talk about gods and such.
This would pertain to when tribal war comes out:
1) I purpose a system where in order to war dec (a deceleration of war) a tribe needs to sacrifice to a god. This would require items like a fire, bear heads, and other such items.
This would put a restriction of the number of war decs a tribe could do, since the items would be limited to a degree. It would also give a chance to the smaller tribes in the area to survive rather than all of them being rolled over by a larger tribe.
2) Same need to sacrifice, but it isn't mandatory; however, if the war deccing tribe didn't sacrifice, there is a chance that the gods don't approve and kill off some of their members during the attack, poison some of the members, and/or take away their energy for X time randomly, etc.
It's like in the books of Iliad and the Odyssey, where the gods do matter and mettle in the lives of us puny mortals.
- Edit -
I guess now thinking about it, this would be cool as well for when/if agriculture comes in and sacrificing for a good year and harvest, etc.