When the Dark Portal was opened, the area around it began to wither. During the Second War, the Black Tooth Grin clan established its bases on this area and was entrusted with the keeping of the Dark Portal.
By the end of the Second War and the destruction of the Dark Portal by Khadgar, the entire Morass was still a swamp. However, the link between the two worlds remained, even after Draenor's destruction, and the damaging effects of the portal continued. This left behind the wasteland of today, which eventually became the barren Blasted Lands. The northern part of the Black Morass, which was far from these effects, remained intact, and thus, has been renamed into Swamp of Sorrows.
The Burning Crusade
This section concerns content exclusive to The Burning Crusade.