There's a lot of great stuff in here, actually. Your suggestions about modern Dwarves being descended from a single family reminded me of Noah's Ark, which made me realize that there might be some fun ways to have the story of the Dwarven planet feature some parallels to the story of the Flood. It could be that the Dwarven Deities warned the Dwarves to get underground before a certain point but only a small number of them actually listened as a majority had turned their backs on the Dwarven Deities. As a result, when the catastrophe hit the planet, only a small number of Dwarves actually survived because they'd actually moved underground. As for the cultural impact of these events, I had been planning on Dwarven cultures being, at present, republics of the Greco-Roman varieties, though with the added element of powerful Guilds which acted as large voting blocs. I could see this being something that got started in the aftermath of the Divine War, with the Guilds originally being founded to ensure that people got all the necessary training they needed to perform various trades that were essential to the survival of Dwarven societies. So, you'd have the Mining Guild for carving out new spaces for underground cities to expand, the Blacksmith Guild for metal workers, the Farming Guild for the underground farms (which will be a magical form of hydroponics in some cases,) and so forth. Over time, however, the Guilds began to use their influence to decide who did and did not get to work in certain trades and abuse their power in other ways. Think of it like a combination of corrupt labor unions and criminal syndicates. The Guilds hold a ton of sway over who gets to be in charge of Dwarven societies. Thus, rulers tend to spend the first part of their administration paying off all the people they bribed into getting a particular Guild to vote them into office. I do know that once access to the Transitory Planes became available, some of the Dwarves abandoned the Dwarven Homeworld, hoping to find a better life above ground on another world. Ironically, most of them would make the Plane of Earth their home, though I hasten to add that the Plane of Earth has Shell Worlds in it. These are planet-sized chambers that are like Dyson Shells, complete with Sun Portals providing illumination, a day/night cycle, and weather patterns. Thus, one can live "above ground" while still being "under ground" on the Plane of Earth, which is mostly solid rock. That's all I have time for, now, but thanks for the feedback! It's given me plenty of food for thought!