Elfs worship the force of the particular biome they live in. So followers of the jungle-force could condem the followers of the savanna-force as heathens.
I honestly don't see that.
To me, Elves going through Holy Wars (when basically they worship nature itself) should represent something just flat out breaking down.
A Corrupted Force, a curse, or something... It shouldn't be a natural course for Elves... Not so much that because they are "Pure" (because lets face it... They are not) but because I think it fits them better.
I was imagining something along the lines of Egan_BW's idea - elves worship Forces associated with different biomes and they oppose one another. Then again, historically speaking, religion is often a
casus belli masking other, more temporal issues, so maybe different elven civs are just faking a Holy War to resolve their crippling mango and cheap cloth financial crisis.
Humans are the only entity that gets its ethics randomized currently (I think), but I'd love to see elves, goblins, and dwarves have some variation as well, to the point where you could have two different elven civs with very different ideas of nature and harmony (it's not hard to imagine an elven culture that isn't down with martial cannibalism).
Ultimately, this comes down to making entities less static, and more fluid, in the sense that entities can split and recombine much as real world sovereign entities do. Perhaps there could be an Elven Schism, or an Elven Reformation, etc.
Whether Forces (or Gods proper) can be corrupted, or otherwise change state, will ultimately depend on how the Myth Arc plays out. We don't really have a solid basis for the nature of gods, aside from the fact that they can only act in the beginning of time (raising underworld spires) or through mortal-built temples. That, to me, suggests that their existence is at least partially dependent on how they are worshipped, which in turn suggests that mortal events (like a war between elven nations) could cause theological changes.
EDIT: historically speaking, being culturally inclined toward "harmony" isn't a panacea against civil war - several Chinese philosophies stressed that concept, but Chinese history is a patchwork of state fission and reunification.