Dragons I often find hard to conceptualize how they actually fit into most D&D worlds on a species level since they can be so long lived, so powerful, and often so smart (not to mention so varied in type). A bunch of worlds have separate dragon lands where they rule, Eberron, Council of Wyrms, Scarred Lands, for instance, but I never really find those dragon specific places as things I would want to directly run a game in. Mostly I run individual dragons in a mostly humanoid dominated land and do not sweat it much, though I am thinking of using something like Kobold Press's Mhaorti Empire for a dragon dominated setting as something offscreen from my homebrew's main setting.