OK so I doubt any of you care to slog through my old writings just for kicks, you are looking for something inspiring or useful that you might apply to your own game or world somehow.
So the original “setting riff” I suppose you could call it for Holothom boiled down to:
1) A bunch of primitive humans (“barbarians”) flee some war-zone and cross some big mountains into some apparently uninhabited lands.
2) The “uninhabited lands” are actually the ancient homelands of the demi-humans (who are either unknown or mythical in the rest of the world). Also full of humanoids and other monsters.
3) After the demi-humans watch the humans for a few centuries and judge them “ready,” the elves and halflings come out and share their knowledge with a couple of human kingdoms.
4) This knowledge gives those human kingdoms a technological and philosophical “jump-start” that allows them to advance faster than the other humans in surrounding lands.
Some of this got slightly modified in later incarnations (for instance once I broke up the Barbarian Migrations into several waves, some humans did have earlier contact with the demi-humans).
So there you have it, the “foundational concept” of the realms of Holothom on the planet Granjor.