Dorcha Geal ("Lost Light") is one of the original Eldar Craftworlds, created before the Fall. When the Fall came, Dorcha Geal set off the escape with the rest of the Craftworlds. But its escape into the Webway was almost too late. As it was entering the Webway, the psychic death scream of theoir race caught the Craftworld, destroying the rear sections of the large city-ship.
The Craftworld escaped into the Webway, heavily damaged. Many of its Aspect Shrines were gone, obliterated in that instant before their escape. Another side effect was the death of many of the Craftworld's psykers. The early discovery of this prevented the loss of their souls, and while most joined the great Infinity Circuit, many of the Warlocks and their Acolytes contined fighting the Great Enemy in Wraithlord bodies. These Warlock Wraithlords came to be known as Spirit Walkers. Their Acolytes were placed in smaller versions of the Spirit Walkers, known as Ghost Warriors.
Perhaps one of the most devastating side effects of the death scream was the loss of the Webway generator. The Craftoworld was trapped in the Webway for millenia, having to fend against attacks from their Dark Kin until they could build a new generator. During this time, the Craftworld's inhabitants became dark and pessimistic. Many joined the Path of the Warrior, and new Aspects were created. These Aspects were the Dark Phoenixes and the Night Stalkers.
The outfits of the Warriors changed as well. Where they had once worn bright colours, the Warriors now wore black body suirs covered by dark metallic armour plates. War became a spiritual ritual, and Warriors began to name their equipment. Achievements of individual Warriors were marked on their armour, runes signifying the dark deed they had grown so used to.
The Warrior squads came to be known as Clannads, "families". Their Exarchs were known as Athairs and Mathairs, "fathers" and "mothers". This brought a feeling of togetherness to the Warrior squads, and they grew to regard each other as their own flesh and blood brethren. In battle the Clannads fought in a more organized manner, but deaths among the individual Clannads were felt more emotionally than they previously had been.
When Dorcha Geal finally left the Webway, it rendezvoused with Ulthwe, a former neighbor Craftworld. The inhabitants of Ulthwe were shocked to see these Dark Warriors who were their brethren. Even the Craftworld was decorated in scenes of war, however elegant. Statues of Khaine smashing his foes stood in gardens. Paintings of Warriors engaged in a Dance of Death with their Dark Kind adorned the Library walls. And from the wall of the Lord Farseer's private quarters, it obsidian handle and wraithbone blade gleaming, hung an ornate brodsword, its blade decorated with runes of Life and rune of Death.
Disgusted, the Ulthwe Eldar left Dorcha Geal. The Farseers of Dorcha Geal knew theat they would never be regard the same by their Kin. The Craftworld pulled off into a part of the galaxy that was barely populated by Eldar, and have had little contact with any kind of their Kin since.