Dwarves

Some millennia ago, not long after Amaranth was first founded; the Dwarves of Amaranth were driven out of their underground citadels by the serpentfolk, who turned them into vast snake nests. Yet more dwarves never made it out of their underground homes. But when they surfaced, they found a city of Tieflings and Eladrin, already waging war against the serpents, and readily joined forces, eventually ending the war some decades later.
Many dwarves delved back underground to try and reclaim their former homes, but found them reduced to dust in the wake of the Serpentfolk's withdrawal. Many were purged of the serpents that still lingered there, but the dream of returning home died there.
The dwarves of Amaranth, to this day, still view their old homes below the earth as a foolish trap, that they build for themselves. When the enemy came, the walls didn't protect them, they just hemmed the dwarves in, with nowhere to go, and no place to turn to. And so even now, the dwarves of Amaranth live outside the east wall, delving into the ground for metals and stone, but always keeping their escape routes open. Nonetheless, they have built a lengthy wall, named Destra's Wall (for the dwarven matriarch who began it) that prevent Malthracion simply overunning their villages, forcing them to fight over it or take a circuitous route around (by which time, dwarven and Amaranth forces have usually amassed).