My setting takes place nearer the equator/south and back in a time when the Yuan-Ti empire is at its apex.
They were former humans living under the rule of evil Nagas. Couatals came from heaven to fight a war against the Nagas. A handful of humans learned magic that allowed them to slay all the Nagas/Couatls, gained their divine power for themselves, and became the first of what we now know of as the Yuan-Ti gods.
The process also turned their most faithful followers into Yuan-Ti: more snake-like depending on how close they were to the gods.
Their temple-cities are in the deepest parts of the jungles, but through Psionic manipulation, assassination via poison, and advanced magic, they have incorporated surrounding human tribes who are vassals, tributaries, and slaves.
Society superficially resembles Egypt/Mesopotamia/MesoAmerica, but has many similarities to dystopian fascist states. Society is stratified, with slaves at the bottom, human sycophants in the middle, and Yuan-Ti on top. Yuan-Ti organize themselves into the elite Warrior/Priest caste which consists of Abominations, mundane warrior/priests consist of Malisons/Halfbloods, and the Purebloods, who are closer to humans and act as administrators, clerks, and overseers for humans.
In most of their cities outside the temple-cities of the south, the population ratio is usually 85% humans, 8% purebloods, 5% malisons, and 2% abominations.
Spies and Psionic mind readers are everywhere, looking for thought crimes. People breaking the law tend to just fall over from poison or disappear and reappear as a mind-wiped slave rather than be publicly executed.
They are very advanced in Magic, although they tend to focus on darker aspects like blood magic, necromancy, curses, and mind control.
Cont...