Sundering Wars
A brutal series of Elven civil wars in Crystal's antiquity, even before the rise of Xsia. They finally ended with the banishment of the Dark Elves to the Underground, and the formation of the kingdom of Kavan--last refuge of the Elves--deep in the forests of what is now Toroia.
The death toll was incalculable, with more than one kingdom quite literally wiped off the map due to the sheer destructive power of the magics employed (magics, it is said, the Elves have since lost), and the earth itself was irrevocably changed. The Great Desert, home to modern day Damcyan, was blasted from a once-verdant forest in the most egregious example. Perhaps more than anything it was this tragic period of Elven history that led to the race's eventual decline.