During the Burning Legion's third invasion, the Knights of the Ebon Blade traveled to the Shadowlands to acquire the Aggregates of Anguish, five tormented essences of powerful souls - Admiral Proudmoore, Soulbinder Nyami, Grand Empress Shek'zeer, Grand Apothecary Putress and Archmage Arugal. Salanaar required these to conjure the Steeds of the Damned for the order's new Horsemen.
One thing that has always been remarkable to me in World of Warcraft is how it brings players together from all sides of life to meet with common goals. I've been playing the game for fifteen years, and have played with gamers with all sorts of accessibility needs. I distinctly remember raiding Serpentshrine Cavern back in the day with an amputee friend Paladin who healed an entire raid of 25-players using a mouse equipped with dozens of buttons. He also competed at a high level in World of Warcraft Arena, as well as any able-bodied player I've seen.
The origins of the Shadowlands remain uncertain, but they have existed ever since mortal life first arose in the physical universe. They span all worlds, including Azeroth, on which Icecrown serves as an anchor to the Shadowlands. There are those who believe mortal souls are drawn into this dark place when they die, remaining there forever. Others hope their souls will go on to a brighter place rather than languish for eternity within the cold confines of the Shadowlands.