While Thrall was liberating his brethren in Lordaeron, Ner'zhul continued to build up his power base in Northrend. A great citadel was erected above the Icecrown Glacier and manned by the growing legions of the dead. Yet as the Lich King extended his influence over the land, one shadowy empire stood against his power.

The ancient subterranean kingdom of Azjol-Nerub, which had been founded by a race of sinister humanoid spiders, sent their elite warrior-guard to attack Icecrown and end the Lich King's mad bid for dominance. Much to his frustration, Ner'zhul found that the evil nerubians were immune not only to the plague, but to his telepathic domination as well.

The nerubian spider-lords commanded vast forces and had an underground network that stretched nearly half the breadth of Northrend. Their hit-and-run tactics on the Lich King's strongholds stymied his efforts to root them out time after time. Ultimately Ner'zhul's war against the nerubians was won by attrition. With the aid of the sinister dreadlords and innumerable undead warriors, the Lich King invaded Azjol-Nerub and brought its subterranean temples crashing down upon the spider lords' heads.

Though the nerubians were immune to his plague, Ner'zhul's growing necromantic powers allowed him to raise the spider-warriors' corpses and bend them to his will. As a testament to their tenacity and fearlessness, Ner'zhul adopted the nerubians' distinctive architectural style for his own fortresses and structures.

Left to rule his kingdom unopposed, the Lich King began preparing for his true mission in the world. Reaching out into the human lands with his vast consciousness, the Lich King called out to any dark soul that would listen....