Some of the leaders are clearly better at warring than others. It seems to be about having the right balance of build unit prob (more units in a stack is usually better), unit type build preference (collateral is good because it means they aren't stuck with one catapult) and attack bravery (needs to be high enough so they take the initiative if they have the advantage in a siege before the unit gets stuffed full of defenders but not so high that they throw all their units away like Shaka) plus DOW chance and the power difference that they will DOW at (again needs to be a good balance between seizing initiative and getting involved in wars versus likelihood of war success).Biggest missed chance for Peter was the peace treaty after he had finally broken through vs Boudica in their first war. The conduct of the war was also terrible. He did have the superior forces needed for a clean invasion but mismanaged them badly.