The Death Knight Arthas Menethil was instructed by the Dreadlord Tichondrius to bring the corpse of the necromancer Kel'Thuzad to the Sunwell, the source of the High Elves magic, in order to resurrect him in a much more powerful form. Transporting his remains in the urn of King Terenas, Arthas and the Scourge began their march across the Plaguelands of Lordaeron to the elfgates that protected the elven kingdom from invaders. The treacherous magister Dar'Khan Drathir betrayed his own people and helped Arthas through the gates. The undead forces subsequently destroyed all in their path, blighting the very land they trod upon. The path they took across Quel'Thalas remains burned into the soil today. Kel'Thuzad was eventually resurrected, and the Sunwell defiled, thus cutting the elves off from their source of magic.
The tainted soil of the Dead Scar draws undead to it and completely disrupts the energy in the ley lines beneath it. The undead presence along the Dead Scar is considerable. Though they are fairly weak, their numbers are enough to keep the Silvermoon Ranger Corps busy fending off the undead marauders. In the Ghostlands, however, the undead was amassed behind the walls of Deatholme, where the traitor Dar'Khan Drathir and his lieutenants commanded the Scourge efforts in Quel'Thalas.
Along the edge of the Dead Scar at the East Sanctum in Eversong Woods, Apprentice Mirveda embarked in a dangerous line of research, one that her own former mentor had lost hope for. She ventured into the Dead Scar by herself to collect samples and see if it was possible to heal the defiled ground. She concluded that her endeavors were hopeless, for the very nature of the soil was altered, and deemed the taint irreversible.
As discouraging as the research results were, they still contained valuable data. A magister needed to review her work before it could be taken seriously. Her mentor Magistrix Landra Dawnstrider found the notes shocking; if they were correct it would mean that the damage to the land on the Dead Scar is irreversible. If that were the case, she believed that it would be one more reason for her race to escape this world and find their true fate in Outland. She notified the Grand Magister right away.
On the Isle of Quel'danas, Eredar warlocks, Wrathguards and pit lords in the service of Kil'jaeden fought in the Dead Scar against the undead remnants of the Scourge. At the northern end could be found the commander of the Legion forces Brutallus, verbally sparring with the blue dragon Madrigosa.
After the end of the Argus Campaign, the Windrunner sisters reunited in the Eversong Woods and traveled to the Ghostlands through the Dead Scar, fighting the undead, until they reached Goldenmist Village.