Commonwealth of Inhabited Worlds
In the fifteen-hundred or so years since humankind first set foot into the void of outer space, much as has been learned, lost, and rediscovered. Spread across an area of the galaxy roughly 150l.y. across, with the Solar System more or less at its centre, humanity is divided ideologically and by sheer distance into a large number of competing allied and rival polities, usually between 1 and 3 in each star-system, bound together extremely haphazardly under the aegis of a pan-humanity organisation called the Commonwealth of Inhabited Worlds.
Mankind is by no means alone in the cosmos, but has yet to discover life on other worlds possessing something comparable to the capacities of human beings. Naturally, though, this does nothing to prevent hope, fear, and rumour, of such discoveries lurking around the corner. The vast bulk of the human population lives in monumental space-habitats, principally because of the ease with which an environment can be controlled and life sustained.
Some 900 years ago (or, ~500 years from the RW 'now'), resentment at the ever-growing 'mob rule' and majority-tyranny of data-driven 'Moderated democracy' that had emerged over the previous 500 years since the dawn of the 20th century C.E., brought about a general war in the Solar System and the institution of a more conservative but more representative government (not altogether dissimilar from that found in many old Earth nations by the 21st century). Gradually such revolutions or reforms occurred in other star-systems as well. The so-called Parliament War or 'War of Cards' (after one of the means by which the first revolutionaries passed messages to avoid detection) resulted in the creation of a number of new competing polities, both in the Solar System itself and across the Commonwealth.
Among these is the Transairy Union, among the largest in the Solar System by population and certainly the largest in terms of space directly controlled - the bulk of everything between the Mars and the heliopause, constituted as a federal, semi-presidential republic...
** PS. Very much a broad-brush WIP, the setting for a novel (maybe, series!?) currently under construction, principally for my own notes, because WA I've discovered is awesome for this, & focussing on one to two specific themes/events mostly for now internal to the T.U. ...**