The one of two reasons for starting war now in H&H is greed. The list of resources is pretty short, though: that`s soil, water, clay and sand nodes together with some wealthy fortresses. The idea is to add more reasons to fight.
In world 6(as it seems the only way to implement this) there should be special rare places which, when used right, can bring some bonuses to a holder. These could be forests, uncommonly rich with beasts or giving home to a rare ones(hey, plain which once in a while spawns horses!), rivers which are the only place where special fish can be fished out, salt caves, mushroom grooves and more. Loot from these places should be special and worthy, to provoke struggle.