The Mitanni Kingdom
This state existed between 1500 B.C. until 1200 B.C., in the are we now call Syria and northern Iraq. Oddly enough, while you may not have heard of the kingdom, you know at least one person from there; Queen Nefertiti. She was reportedly a princess from there, and was married off to the Egyptian Pharaoh Amenhotep IV, to improve relations between the kingdoms.
There’s not a lot else that is known about the kingdom. They supposedly believed in things like Karma, reincarnation and cremation, and were a highly influential civilization. They were conquered by the Assyrians and whatever knowledge wasn’t saved or catalogued by the Egyptians, was lost.