Yeah, I think you did good. Most of our planning is still pretty abstract at the moment, so it doesn't matter too much. This is the important part.

I think I would rather avoid making gods the main reason for the conflict. Unless the gods are very significant in everyday life (which is, of course, a possibility), we might as well go with "a reason long forgotten". It has the same amount of significance. Most conflicts in our world have reasons to have begun, even if they are different for both sides. People tend to keep track of reasons to hate someone else. 

The problem with slaves is that the conflict would be over a lot quicker. A fight for freedom is good, but after that point it goes back to "business as usual". American history as my evidence. 

Cultural reasons/ differences in customs are usually a good one, as is supposed assassinations, if the supernatural populations has kings/emperors. Or, if we want to make gods very significant, we could go back to some godly reasons.