The Galactic Empire
While most records from that era to survive point to the ‘dark’ Esper tradition being the origin of the Galactic Empire. The truth is that a human seed ship established a remote colony just outside what had been known space, there they found ruins from one of the prehistoric governments. Either before or after a single faction took control of the colony. That was the state of things when a group of exiled Esper Knights discovered them. Since much of the ancient technology responded only to psionic powers these new comers would eventually take control.
Under this leadership the strong would rule through a series of ‘guidelines’ which directed their behavior. The weak were enslaved to perform menial labor. They would soon develop technology to nearly rival The League of Systems and within a few generations expanded into known space. They would conquer everything in their path enslaving or adding as they went. It took nearly a decade for the League of Systems to respond to these attacks and doing so began the Civil War Era.