Background Information
Humans were contacted by an advanced alien species (the Hyar) who introduced humanity to the Galactic Community. Humanity integrated well, showing special adeptness at military matters, until they were well-represented in every branch of the Community Defense Force. Within two centuries the worse elements of humanity overthrew the Community and established an empire. The Empire lasted two centuries and took another to come apart. The remnants of the Empire coalesced around several power centers and formed the current collection of human-centered or dominated polities. Other remnants of the Community, most of which are non-human dominated or centered, also continue to thrive.
The Hyar originally believed that humanity was a vibrant and dynamic species that would be a strong ally against a xenophobic species from the galactic core that threatened the Community. They were right and humans fought hard alongside other species. They also learned everything they could from other, older species and the imperialistic ”Humanity First” group used that knowledge to establish the Empire. The Hyar disappeared en masse as a species at the beginning of the Imperial drive and have never been seen since.
Human (or majority/dominated) Polities:
The Federated Alliance, an attempt to recreate the Galactic Community, a heterogeneous collection of worlds with great diversity of species, centered on Earth and the core of the former Empire. Despite the great diversity within the Alliance, it remains majority (if only barely) human in population, and humans predominate in Alliance military and governmental structures. The Alliance is the largest power in erms of number of worlds, industrial capacity and defensive might, though it remains about half the size of the original Community.
The Solian Empire, a prejudiced, racist, human-superiority empire that is the spiritual successor to the Human Empire. Several non-human worlds are enslaved within the Empire which is approximately one third the size of the former Human Empire. Its capital is the industrial world of Bessemer. The emperor claims descent from the former Imperial family.
The Accord of People, a human polity of one star system (with many colony cylinders and two worlds) that is wholly surrounded by the Alliance, and cooperates frequently with the Alliance and the Republic, but is not a member of either. Their system is closed to most outsiders, and it is rumored they are technologically ahead of the standard.
The Holdings of Maxentius, a dictatorship that controls several systems in the border region between the Alliance and the Solian Empire.
Additionally,
The Galactic Republic, a remnant of the Galactic Community that resisted the Empire and remains. Heterogeneous and diverse and humans are a small minority. Roughly on par with the Solian Empire in size and resources.
The Kingdom of Randu, an alien kingdom governing several systems on the fringe of Republic space.
Unaligned Space is an amorphous tangle of systems in and around the border regions between the other powers. There are many single-system or single-world polities in these areas balancing diplomatic tensions to maintain their independence. The types of governments and adherence to law, morality and sophont rights among them vary wildly.