Or perhaps something that could differientiate the cultures that could be used for trades also:
Say in a combat sense, one could have better weaponry, the other better defense.
Say Rayya has stronger weaponry. Their style of weapon crafting yields stronger or sharper weaponry which results in a higher Attack yield.
Ascendant with stronger defense. Their metal is denser and provides higher protection(or defense), inc. Shields.
Even access to different metal types found in each biome could influence this in the future.