The deep dwarves, the ones who had never left the safety of the mountains, built their homes within the bowels of the earth. For centuries, generations lived in their vast subterranean cities, working, living and dying under the ground.There was less of the latter than the former two, because the dwarves were a long-lived race, though they reproduced slowly.
Indeed, so long did they live and so slow did they die that the dwarven cities eventually experienced a lack of room. Unlike the cities on the surface, they could not simply expand outwards. They had to dig; and often, they had to dig down.
So they dug down. They always dug down. Down was dark and deep, filled with welcoming darkness which the dwarves could see through with their darkvision, and the comforting presence of stone all around them.
It was their element.
It was their salvation.
It was their doom.
One of the deep shafts struck… something. Nobody knew what it was at first. They only recognized it by its handiwork; darkness, and death.
The newly-founded holds at the base of dwarven civilization were the first to fall. Entire vaults and cities vanished into the darkness. No longer was darkness an old friend; it soon became a thing to be feared, and even among the dwarves — who could easily see in the lightless depths — it soon became a common practice to light torches and shed illumination everywhere.
This was wise. In places without light, dwarves might walk fearfully through the darkness and never emerge again.
The first sight of their enemy came by chance; a blood-curdling scream drew a squad of dwarven warriors with lantern-shields and axes; they found a many-legged… thing, dragging the severed upper torso of a dwarf away in its wicked jaws, chittering mindlessly as it slithered into a crevice seemingly too small to hold its body.
Thus began a great campaign to illuminate the dwarven cities. Entire workshops labored day and night to produce lanterns and magical lights. Soon, they were everywhere, and their foe was forced into view.
The dwarves would soon come to regret this.
Deprived of hiding places, their shadow-dwelling adversaries decided on a frontal attack; a nearly-limitless horde of multi-limbed monstrosities boiling forth from the depths of the earth. Axes dulled, armor broke, and crossbow bolts ran out and the horde continued pouring forth. Still, with blood and sweat, the dwarves halted the advance of their foes, which they called the Darkbrood.
(TL Note: 闇種)