The Underhalls were meant to be the second chance and rebirth of the Durgheil people in Avanor, yet their kind did not take too long before they started to turn on each other for conquest, resources and the very valuable minerals of the deeper tunnels. Ambitions saw the rise of many dwarven kings, most of whom could not unite the dwarven people under one, single kingdom; leaving Thane Councils to rule over the many independent underground cities.
When the Black Blood Curse spread from the city of Orthavir, many of the Underhalls' tunnels, halls and cities were abandoned by their inhabitants or conquered by the Darkborn. The increasingly rising strength of the Darkborn dwarves, who were created by the Black Blood Curse, saw the fall of many dwarven cities, until only a few remained. Most of these cities were on the upper levels of the Underhalls, and a few of them still stand to this day; having established strong defenses against the dangers that now lurk within the deepest reaches of the dwarven tunnel networks.
The dwarves who live in the Underhalls are dominantly of the Stone Clans, though there are a few Iron Clan descendants from the days when the Barador Empire fell and crumbled into the kingdom it is today. The dwarves' lives are rough and hard, as surviving underground is made dangerous by threats ranging from tunnel cave-ins to Darkborn raids to the violent bickering of their fellow brethren. The cities hold on merely by fragile, thin alliances, and often enough there are ambitious would-be-kings who wish to unite the cities for their own purposes; often on the promise of retaking the deeper levels of the Underhalls from the Darkborn. However, none know where Orthavir's (where it is believed that the Darkborn home is) location is at, since most maps of the Underhalls only cover a fraction of the vast network. Rumours say that Orthavir found its way into the Underneaths; where beings of unimaginable terrors reside.
Aside from the Darkborn or other dwarves the Underhalls are home to many other dangers and creatures; many of which have yet to be discovered. The Aedh Shavai elves, after their exile from Daln Ashelaan, traveled into the Underhalls and established their new home within the abandoned cities of the Durgheil dwarves. While many of their kind were forced to the surface again by the Darkborn, some of their cities still remain not only within the Underhalls, but deep within the realm of the Underneaths.
Some orcish clans and goblin tribes also reside within the Underneaths. Their kind are far less peaceful than their surface brethren, as the challenge of surviving underground has made them creatures of desperation and violence. The Underhalls is a place where only the strong survive; leaving little room for trust and peaceful ventures. Even so, many surface-dwellers travel into the Underhalls in the hopes of finding anything from rich veins of ore to recovering lost dwarven secrets or treasures.
Although they are referred to as the Under-kingdoms, the dwarven kingdoms of the Underhalls only hold less than a handful of cities each; many of which only act as mines or outposts that support their capital city. Many of the cities within the Underhalls have been abandoned for hundreds of years, and the Under-kingdoms are often locked in battle with each other for the right to reclaim various cities known to be rich with resources, treasures or knowledge. Although war is something of a rarity between the Under-kingdoms, conflicts sometimes spiral out of control due to their long-lived rivalries. The Under-kingdoms mainly survive through trade with the surface nations; something which tends to cost a great deal of coin and resources. As such the importance of recovering long lost outposts is paramount for the survival of the various Under-kingdoms.