The War of Horrors
Xoriat, the Realm of Madness, is home to the daelkyr. This chaotic realm defies description, and non-natives which dare to glipse it risk horrifying, permanent insanity. 9,000 years ago, Xoriat became coterminous with Eberron, and the continent of Khorvaire was overrun by daelkyr and their aberrations. This started the Daelkyr War, which destroyed the Dhakaani Empire.