One of my proto-settings, should I ever run a new game, has a Dragonborn empire as the primary civic-culture force. It's highly distributed because it was founded by a warlord who discovered bow to reactivate ancient teleportation circles, and used them to conquer multiple city-states by moving way faster than any other army could possibly replicate. She ser herself up as Empress and her descendants continue to rule (with varying effectiveness). Adventurers are often hired to investigate the beast-riddled ruins across the continent in hopes that they'll find new circles to reactivate. Nobody knows who made the circles originally. Humans have literally only just arrived on the continent and are seen as Really Weird Looking, like a strangely beefy changeling or a strangely thin and scaleless dragonborn.
Another proto-setting for 13A specifically is set after a war between an aggressive dragonborn empire took advantage of a freak natural disaster to finally conquer the human-led league of various races on another continent. (Think Persia vs the Athenian League; these humans aren't really good guys, holding effectively imperial control while making a pretense of having an equal alliance, but the dragonborn are absolutely conquerors who want to force fealty upon the whole world.) Knowing it was only their now-lost navy that protected them from a land invasion they WOULD eventually lose, the humans used their last-ditch effort, and performed a massive blood-sacrifice to summon the powers of hell. (Only using slaves, of course, so it's tooootally okay, nothing horrible about it!!!) This made a grand contract and literally tore open a mile-wide portal straight to hell. The devils upheld their contract flawlessly; they never attacked a single human unless that human attacked first, and they drove out the dragonborn within a span of days. But the thing is, they also killed all sorts of NON-humans...and there were a lot of humans who were violently not okay with that. The Icons eventually addressed the problem, but only after something like half the world's population had died and the remainder were on the brink. Humans exist but aren't a majority. Tieflings are descended from those who participated in the blood sacrifice that caused the Great Mistake, so some fools take it out on them even though the perpetrators all died over a thousand years ago. Most dragonborn feel partly responsible, and thus feel a drive to fix the world in some small (or not-so-small) way to make up for it. The dragonborn homeland continent would be the primary setting, so while humans are around they're uncommon.
