The Nerubian Empire was the home of the Nerubians until the Lich King defeated them. Parts of it, once an underground network that stretched nearly half the breadth of Northrend, can still be found beneath Northrend.
After the Azj'Aqir, the Empire of the Aqir, was shattered by the Gurubashi and Amani Trolls, the nerubians fled north and founded their empire in the northern wastes. It's unknown what effect the Great Sundering had on it, but they developed to a high culture with great architecture and created an kingdom beneath the frozen wastes of Northrend. The capital was called Azjol-Nerub, sometimes generalized for the whole empire.
War of the Spider
When the Lich King became stronger, he began to battle with the Nerubians in a war called the War of the Spider. After ten years of fighting the Undead managed to enter the kingdom and brought its subterranean temples crashing down. Most Nerubians were killed and resurrected, the surviving nerubians hid deeper.
The remains of Muradin's dwarves, led by Baelgun Flamebeard conquered an entrance to the empire and founded the Doorward. When Illidan Stormrage used the Eye of Sargeras to destroy Icecrown, the earthquakes freed the Faceless ones, which took over a part of the kingdom. The nerubian survivors and the dwarves were mostly killed when Arthas went through the labyrinth to reach Icecrown Citadel. Arthas also destroyed most traps and treasures, which were still hidden there.
The Lich King, the Eye of Sargeras and the death of the Forgotten one made most tunnels and buildins collapse, so only small parts are left. The former great empire is now inhabited by some surviving nerubians, undead minions of the Lich King, and some Faceless ones, which have recently been reinforced with Twilight's Hammer clan members.
- Doorward - entrance somewhere in Northrend
- Pit of Narjun - entrance in the Dragonblight
- Azjol-Nerub - the capital
- Upper Kingdom
- Shadow Web Caverns - somewhere on the way to Icecrown
- Icy Depths - beneath the Crusaders' Coliseum
- Naz'anak: The Forgotten Depths - beneath Icecrown