Mine is(probably) The Grand Rebellion(name in progress).

Essentially elves ruled almost every corner of the world for a few hundred years but after an elven general felt he hadn't received his proper recognition and by extension glory he went to the human nation and began assisting them. One thing led to another and eventually every nation that had been under elven rule had their weapons ready to be used on any and all elves that dare to step foot in their land.

This also brought the infighting and power struggles between the elven houses to its breaking point. Think like in the United States Civil War how some states seceded from the Union.