The Empire of Bone & Rot

The Empire of Bone & Rot, was an empire that existed in the Dawn Era. It was originally a small group of connected city states past the northern mountains of the Kingdom of Neoko. The cities were all dedicated to the sun god Sepikstola and were predominantly populated with yuan-ti. This civilisation would fall swiftly to the treachery of the vizier of the civilization's king known as Sha’enzazuu.
Little is known about Sha’enzazuu, what is recorded is that he managed to manipulate his way into the king's inner circle, before convincing the king to partake in his private religious ceremonies to Sepikstola. Unfortunately he actually was performing dark rites connected to the Demon Lord Orcus, who had become the vizier's patron. Overtime as he gained more power, Sha'enzazuu removed other advisers or competitors for power until he was the sole power behind the throne.
The rite had become more public, and began using the populace as material for rituals. Sepikstola began to notice however and with it divine retribution. Unfortunately it was not quick enough as a ritual was performed that used the king as the core sacrifice. With this done Sha'enzazuu ascended to lichdom and crowed himself king of his empire of bone and rot. The populace replaced with undead servants.
After a number of centuries of conflict, with Sepikstola leading the charge of his loyal followers, the forces besieged the largest of the temple cities. The force managed to interrupt a rite to allow Orcus into the plane and Sha'enzazuu disappeared without a trace. But before all the remains could be razed the Dark One came to the plane.
Now the temple cities lie abandoned with some undead creatures and many secrets hidden within for those bold enough to investigate them. Fe journey to the northern territories that include the empire and not even the Shadowland has spread this far. Meaning the land is locked in seeming stasis, while nature reclaims its due.