At one point the humans defeated the Sidhe, and Manus, the Serpent Mage of the humans, used his magic to take away the Sidhe's souls.
Then, decades ago, there was a war between the Sidhe and a powerful Breed sorcerer known as the Isomage, burning a large portion of Sidhedark and creating an area now known as the Blasted Plain; the upheavals also released some of Adonna's unwanted creations that it had hidden underground.