Most science-fiction worlds are really rather boring with how the various species are politically organized. Every species has a single state, and that is it. Or you might have quasi-federal systems in which each species constitutes one federal state. One could look deeper into how this might have originated in an American cold-war mindset, but I think it’s pretty self-explanatory. And also not really interesting.
Thinking about how species with multiple states could be organized in a space setting, I came up with the following five types:
In the first case, we have the simplistic unified state that collects all the planets inhabited by a species under a single government. I think it does have its place in a setting that isn’t about big empires fighting each other, but as a kind of government that most other species see as a strange oddity that defies the common logic. You find this in all of the big powers in Star Trek. Even the Federation, which is a singular state that includes all the homeworlds and colony worlds of several species.
The second example has a politically unified homeworld, with its own colonies and outposts, but several of the full size, self-sufficient colony worlds have gained their independence as their own sovereign states. In such a model, it seems quite likely that relationships between the independent colonies and the homeworld might be somewhat strained or hostile, as the homeworld clearly still has a policy of maintaining direct power over some colony world. This is the political order that we see in The Expanse.
In the third example, the homeworld is a unified state, but all the self-sufficient colony worlds are sovereign states as well. The homeworld does not have special status, other than likely having the largest population. I think this model would work quite well for loose confederations, where the homeworld is used to granting colony worlds independence once they reached a certain size. This only makes sense if the homeworld believes it will still get the full economic benefits from having funded the colonies’ construction. Something very close to this model can be seen in the human Systems Alliance in Mass Effect, which I think is actually a federal republic based on the United States, in that the parliament is located on a space station that is not part of either Earth or any colony.
The fourth example is where things start getting really fun. You have several sovereign states that each have their own colonies. I think this might be very well in our future at the end of the century, when the economics of space exploration make joint international research stations like the ISS no longer a necessity, and nations can fully fund their own separate stations. This is what I have in mind for the less advanced species, but much of my ideas for this setting are about seeing past the blind determinism of progress that defines most of 20th century sci-fi, and so I think I’ll also have some very highly advanced species that have this system anyway.
The fifth example is a variation of the fourth. In this case the homeworld still remains unified, but some of the colony worlds have become independent. I plan to use this only for one species, because this is probably the messiest of them all.
All the examples here are only with up to four states, but you could easily have 20 or 30 states for a single species. But that would be practically impossible and of little use for anyone, so more than four or six would be overkill. I also don’t plan on writing up all the star systems of known space, only maybe 30 or so. So of the potentially 50ish sovereign states in known space, I’ll probably fully develop only half a dozen at the most.