Shadowfell

Shadowfell is a plane of existence filled with darkness and shadows. It is a rocky and barren place, filled with abandoned settlements and scattered siege equipment, and the scars of a battle that has seemingly lasted forever. It now lies almost entirely abandoned, as very few creatures would willingly live here.

The Battle of Eternity
Shadowfell, a long time ago, was the site of a massive battle, which waged on for longer than any mortal could remember. Both Hadius, god of magic, mystery and music, and Daxion, the god of destruction, had been trying to conquer it and claim it as their own.

Massive armies of demons seeped into Shadowfell from the Lower Planes, led by Daxion, and large numbers of fey from the Feywild led by Hadius.

To aid his demons, Daxion summoned the Minotaurs, Centaurs, Orcs and Tieflings. In response, Hadius created the Gith, Loxodon, and Yuan-Ti.

The Shadowfell Incident
In the ancient history of Irion, Hadius banished a large number of elves to Shadowfell. The elves, being blessed by Hadius with powerful magic, deeply upset the god, when they chose to worship Raegora exclusively. This filled Hadius with great hatred and envy, because at that point of time, the gods looked down on Raegora, who had never even assumed a material form, and was considered weak, and not generally worshipped by anyone up until recently.

As punishment, he turned their skins pale and dark and their hair white, and gave them red eyes that are better suited for the dark, and banished them to Shadowfell, where they were forced to battle Daxion's troops of evil, until the end of time.

Or, that is what Hadius had hoped would happen. Instead, they prayed, and prayed, until Raegora materialised herself in the form of a Drow woman.

She convinced the creatures of Shadowfell to stop fighting for their respective gods, and instead live in peace, under her guidance. A vast majority of the creatures accepted her offer, and after some more decisive battles with remaining resistance armies, all the demons, fey, and creatures loyal to their gods, were driven back to their respective planes.

After the incident
After the incident, knowing that the barren, infertile, and battle-scarred lands of Shadowfell would not be a good place to live for anyone, Raegora set her worshippers free, and sent them to Irion.

Shadowfell is now widely accepted as Raegora's domain, and no further attempts to conquer it have been made.