Of the races of elves, the eladrin suffered the most during the Cataclysm. The lost their world spanning empire when the Eldrich Horrors spread their spite across the world. They lost their identity as those who survived retreated to the ruins of their estates. They also lost their faith as even the clerics could not call upon Corellon Larethian to heal the most simple of wounds.
The sylvan elves would point to the loss of faith as the most tragic loss suffered by the eladrin.
Many years went by before Corellon would respond to the prayers of the clerics, and in that time almost half of the remaining eladrin went mad from grief and began a crusade to eradicate their own kind and were labeled “Dark Elves” for their deeds.
Thankfully, there was enough strength left in those sane eladrin to fight back against this new evil. What is left of the eladrin empire are isolated city states, underpopulated, and decaying. Those eladrin who venture from their home are warned about the Dark Elves.