The Midlands Histories
The elves now known as drow were once eladrin. Long before the Fracturing, a group of eladrin from the Unseelie Court ventured to the far reaches of Faerie, where the darkest shadows dwell. They sought to determine whether the darkness could be used in their eternal machinations against the Seelie Court. What they did not bargain for was that such power would come at a cost. They moved through the shadowed lands, encountering umbral creatures and attempting to steal their powers.
Towards the end of their travels, the eladrin came upon an angel of darkness. They trapped and tortured the angel, until at last it offered the eladrin an exchange. For its freedom, they would be given knowledge and control over shadows, but at the cost of their own fae powers. Though some declined, most agreed, and in an instant they found themselves no longer able to bend the world to travel through it. Instead, when they attempted to do so, shadow stuff enveloped the space around them. They released the angel and returned to Mithrendain, no longer recognizable as eladrin.
It was a long time before they were accepted back into the Courts, and to this day many drow remain Courtless as a result. Those who did rejoin the houses of the High Courts dwell mostly among the Autumn and Winter houses, though they never regained full status in either assembly.
It is rare to see a drow in the middle world. Those that do cross over are often on missions for their Houses.