The Great Underground Empire refers to the latter period of Quendor, when its rule influenced both aboveground and underground.
Under the Flatheads it became a mighty kingdom of wonderous sights, carved right into the bedrock of the earth, with a tremendous wealth, and powerful magic.
During the reign of Lord Dimwit Flathead he became the first to call Quendor "The Great Underground Empire," which became a designation preferred to Quendor. He also renamed the Great Sea as "the Flathead Ocean." Preferring the Eastlands, he moved the Empire's capital to Egreth to Flatheadia.
In a raw act of excessiveness, Dimwit ordered the construction of a nine-bloit-high statue of himself, an act that angered the powerful mage Megaboz.
During the feeble-minded reign of Dimwit, after countless years of decadence and overtaxation, in 779 GUE the great wizard Megaboz cast a mighty Curse. This Curse killed the Twelve Flatheads. His successors did their best to uphold his tradition of excessiveness. The high level of taxation continued, although the money was increasingly spent not on massive construction projects but on extravagant parties and long vacation trips for members of the Royal Family.
In 883 GUE, brought about the collapse of the Empire and the destruction of Flatheadia. The underground caverns fell into disuse, coming under the power of the First Dungeon Master; the Royal Treasury was sacked, and everyone moved somewhere else.
The area is now called the Land of Frobozz, after its largest province. Evil times came when lords made war against each other as every warlock in the kingdom attempted to gain control, the most powerful fo which being Krill. Syovar helped recreate the ancient Knights of Zork to help bring order to the land.
With the defeat of Krill, and then Malifestro, peace returned. Ruling from the Castle of Zork Syovar attempted to unite the lands and raise again the Empire; explorers rediscovered new areas of the old underground caverns, Flood Control Dam #3 was visited again, and the Mines of Zork once again operated, producing coal and diamonds. Syovar inspired respect to all the leaders, and they eventually agreed to meet at Quendor, an old city in the northlands, to sign the Treaty of Quendor, proclaiming a union between the lands. As the conference approaches, a truce between all the warring neighbors has been observed.