Early in the conflict, the Cult of the Damned under the direction of Kel'Thuzad unleashed the Plague of Undeath on the northern nation of Lordaeron, tainting the grain from Andorhal, the primary distributor of grain in the northern provinces, and shipping it to outlying villages and towns. The virulent plague killed thousands throughout the provinces and raised them as mindless undead in the service of the Lich King, and caused the land to become tainted, the plant and animal life becoming diseased. A small resistance, led by Prince Arthas Menethil and Uther the Lightbringer of the Knights of the Silver Hand, were able to destroy the infected granaries and temporarily halt the spread of the plague. By the time of Arthas' eventual fall, beginning with the Culling of Stratholme and coming to its climax with the murder of King Terenas, not one living human remained in northern Lordaeron.
The Blackened Woods of Quel'Thalas, having already suffered from the effects of dragons' fire during the Second War over a decade earlier, also became tainted by the plague after the fall of Lordaeron, during the Scourge's march to the Sunwell. Seeking to give the Scourge as pyrrhic a victory as possible, the elves put their forests to the torch. Today the region is known as the Ghostlands, and is home to the major Scourge holding in Quel'Thalas, the fortress of Deatholme.
Following the Scourge's defection from the Burning Legion after the Third War and the later splintering of the Forsaken, the Plaguelands became divided between the minions of the Lich King and the new followers of Sylvanas Windrunner. To this day, the Scourge continues to corrupt the Plaguelands, spreading the Plague of Undeath from strategically-placed cauldrons that taint not only the land, but the air and the wildlife as well.
There are many others besides the Forsaken and the forces of the Alliance who battle the Scourge in the Plaguelands. The Scarlet Crusade, an organization of maddened zealots who attack anyone who opposes them as fervently as they destroy the undead, has taken control of the few surviving towns in the region, such as Hearthglen and Tyr's Hand. The Argent Dawn, formed by former members of the Scarlet Crusade who opposed its corruption, also have a major presence, striking against key leaders and locations throughout the Plaguelands.
In lore, this is where the dread citadel Naxxramas stood, and with it Kel'Thuzad's reign was enforced and undisputed. With the help of the Argent Dawn, Darion Mograine infiltrated the floating Scourge citadel and tried his luck at bringing it down. He ultimately failed, losing his life in the process. However, he managed to free his father, Alexandros Mograine (formerly the wielder of the Ashbringer), from undeath, finally giving his spirit rest. Without him the dark fortress was left severely weakened as he was one of The Four Horsemen who led the military forces in Naxxramas. And so, with this in mind, the Argent Dawn led an all out assault on the fortress and defeated Kel'Thuzad, but failed to actually kill him. The Citadel ended up "vanishing" from the Plaguelands not too long after. Unbeknown to the Argent Dawn, Naxxramas was summoned back to Northrend, to lay seige to Wintergarde Keep. It was only to be stopped by the strong will of Halford Wyrmbane, commander of the 7th Legion. And as last time, the adventurers came to the rescue, liberating the necropolis and finally slaying the vile Kel'Thuzad, along with the rest of his forces that resided inside.
- Western Plaguelands
- Eastern Plaguelands
- Tirisfal Glades
- Northern Lordaeron, a closed zone.
- Ruins of the Scarlet Enclave, technically a part of Eastern Plaguelands.
- Silverpine Forest (Note: Silverpine Forest is usually considered part of the Plaguelands, but not always, because there are many places without Scourge soldiers, but their influence is evident. Also, World of Warcraft Master Guide: Edition 2 says that the Scourge have a "loose and rotting hand" over Silverpine.)