Every Holy War would reset the balance of power between the various races. Not only would the power balance be reset among mortals, it almost always included the True Gods as well.
Nobody was truly immortal. Not only humans, even beings as powerful as the True Gods had their own mortal enemies and insurmountable obstacles. They were fated to fall one day as well, although they would take many lives with them when they fell.
With the fires of the Holy War stoked, order almost completely collapsed, and the suppressed feelings of anger and revenge finally exploded. There were those that hoped to benefit from the war, or those that cursed their enemies and swore revenge. When these "divine" existences began encouraging their own forces, it was only natural that chaos would reign.