The dark elves were originally one of the family groups of elves that lived on the Elven Isles. They were banished over a minor difference of opinion between their patriarch and the other heads of noble houses. Mainly wither or not the study of elemental earth should or should not include tapping into necrotic energy i.e. Death Magic.
The Dark Elf Patriarch (Haelirin) Gave a blood oath that his family would destroy the other family lines and unite the elven Isles under one banner. The other great families responded by cursing his family line to outwardly exhibit the darkness of their patrons heart. Which is why the dark elves have a different outward appearance from the other elven family lines.
Expulsion from the elven isles altered the psychology of the dark elves from their fair skinned cousins in several ways. First and foremost, the dark elves care little for elemental magic. Living away from the scrutiny of the other family lines has left them free to experiment with whatever power they choose. This has lead toward more divine casters among the dark elves then any other species. Additionally the trend that all elves share to be conscious of blood lines has been heightened to an obsession with genealogy, and ancestor worship. Any dark elf can tell you his relation to each of a dozen ancient elven heroes, and if you let him; he may rant about how depletion of those mighty bloodlines has lead to the degeneration of his species.
The Dark Elves only current city is known as the Dark Elf War Camp and is located to the extreme north of Shea. It is unknown how the Dark Elves survive in the Deep Forest where the Feywyld is meshed together with reality. It is also unknown how many Dark Elves there really are, a secret they plan to keep until the time is right.