Re: Birthright-style in Faerun?
With apologies to Forgotten Realms grognards / scholars. I know I'm being very general, but if the OP is interested he can look into it more closely.
In a nutshell:
There was something called "The Time of Troubles" (which was how TSR explained "out of game" rule changes "in game" when they went from 1st to 2nd edition). The gods were sent to the material plane by Ao to learn humility in mortal shells.
One of the gods, Bhaal the god of murder, foresaw his own demise and "spread his seed" far and wide. After his death his progeny grew up and slowly learned that they carried a piece of his divine power. Whenever they killed a sibling they gained some power (very Highlander-ish). The video games followed the protagonist (a Bhaalspawn) as he dealt with being a semi-divine being who got to chose his own destiny (for good or evil).
This all took place around the City of Baldur's Gate and later on in Amn and beyond, though it did leave things open that there are many more Bhallspawn wandering around.
You could use Bhaalspawn in place of Blooded characters in Tethyr (or wherever) as de facto Regents and stay close to the "divine right" aspect. Heck you could have other gods that had the same idea as Bhall and also have other Bloodlines (Mystra, Mrykul, Bane, etc...)