Well, I have to say that working on my own campaign setting (Ironbound: Chains of Phaetos), the dychonomy has shifted quite a bit. Originally, it was largly human dominiated, but as I've gotten into refining the setting a number of other races have come to the forefront. Elves have their empire, the dwarves have theirs, a lot of humans have freed themselves from dwarven rule. Drow are not from the underdark, but rather from the dark side of the planet (Phaetos is tidally locked).
I've really been trying to work out how these races are culturally different. For instance, elvin culture borrows heavily from Chinese and Japanese culture and history. Dwarves are Roman with a viking base instead of a greek base. Gnomes no longer have their empire, but their culture is a blend of Aztec and Egyptian. Humans have a tendency to show up everywhere, and often adopt the cultures of the other races when they are in the minority. The other races have more than one ethnicity, too - same stats, but for instance, the elves have an ethnicity that is lawfully aligned and another that is chaotically align.
As a Pathfinder-compatable setting, there are a lot of racial options between core and the two bestiaries. How many of these options will be defined as playable...I'm still trying to decide on where to draw the line, or if I really should not draw a line and let the Game Master decide what races are valid for player characters or not. Not every race is going to have their own Empire, but I want Phaetos to be a setting that is as expansive or as narrow depending on the needs of an individual game.