So after deciding, that the story would take place underground, that Humans don't exist anymore and that the major enemy at the start would be the Undead, I wondered what would be the major races underground.
I will start by giving you the finished list first, then explain the different picks in dedicated chapters after talking a bit about their society.
----------------------------------------
Dwarves
Elves (Azugni)
Dragonborn (Draknadan)
Kobold (small Draknadan)
Bird People (Ugol)
Gnomes (Thultast)
Olms (they are giant worms)
Argathen (Essentially pale underground Giants)
Umbrals
Ruin Dwellers
Zirigma
----------------------------------------
So first of all, the things in the brackets are either there to give an idea about what you are reading about (like with the Argathen and Olms) or to give you the name the Dwarves use for the given race.
So to give some general ideas about their society stuff, the Dwarves are **The Major race** underground. At their high point, around 1.5 million dwarves live in new Thymia, they make out about 50% of the population. To give the short version:
----------------------------------------
The Dwarves settled in New Thymia after losing their old homeland and so were the most vigorous settlers. At the start, a democratic Theocracy was established, where the high Abt of Karg Bador, the southernmost City. He held the highest office of the Adalharaz, the Council of the Cities. 80 Years later, a new Influential Merchant family, The Stonehearts would rig the election for the new highest officer and they became effectively (and later actually) the Kings of this new Kingdom/Council thing.
If you encounter this narrative on Amazon, note that it's taken without the author's consent. Report it.
Even after this, the Kingdom would remain quite decentralized, With only the Council being able to influence another Cities decision and in the end, 7 cities would be able to gain a seat on the Council, with the council always needing to agree to their inclusion.
Many Years after the Kingdom had established itself and a balance of power settled in, the Undead invasion started under the Lich King. The Kingdom had been completely surprised when it was invaded. The Kingdom was Months away from other societies, that were threatened or attacked by the Lich King and there were few traders travelling to it. Then, as the attacks started, the Kingdom would lose nearly all of its Cities and most of its Population.
With the fall of nearly all Cities of the Adalharaz and the need for revenge, The Stoneheart family were able to firmly establish their power over the Kingdom.
----------------------------------------
Now this story tells us a bit about the society and history of New Thymia, but it also leaves out quite a bit, like:
Why are 30% of the people in New Thymia bird people and why would elves even want to live there? This and more will be in the Next Episode of Dragon Ball Z Chapter.