Background for yet another story.
As a general rule, interstellar travel was originally only possible through gravity points – locations where, with the proper technology, a starship could transit instantly from one star system to another. (Not unlike the Starfire universe.) Only a handful of races managed the lucky combination of being born in a star system with a gravity point and managing to master the technology. Those that did rapidly expanded down chains of gravity points, establishing long gangly political units that often overwhelmed races that failed to develop gravity point technology,
Everything changed roughly 4000 years prior to humanity’s first contact, when the Tokomak – an alien race originally heralding thousands of light years from Earth – developed the gravimetric FTL drive. The drive worked by creating a series of mini-transits that, outside a star’s gravity well, allowed a limited form of FTL travel. Although very slow at first (original versions of the drive took weeks to cross a single light year) rapid improvements gave the aliens a chance to escape the tyranny of the gravity point network. In addition, where prior use of the gravity point network identified the network to an intelligence spacefaring race native to the newly-discovered star system, the drive was easy to protect from capture and duplication. The result was largely inevitable. Within 1000 years of the drive’s development, the Tokomak had colonised or conquered a sizable empire.
The Tokomak tended to divide races into tiers, depending on their development at the time of conquest. Tier One (gravity-point capable) were generally treated reasonably well, although incorporated into the united empire. Tier Two (spacefaring, but not interstellar) were generally used as techs or servitors. Tier Three (non-spacefaring) were used as slaves, when they were used at all. It wasn’t uncommon for the Tokomak to occupy their world and displace the locals, when they were interested in taking their planet for themselves.
Although the gravity drive ensured they no longer needed to rely on gravity points, the economics of interstellar travel continued to dictate that stars with gravity points (particularly multiple points) remained economically important. Indeed, though interstellar charts showed vast regions of space belonging to the Tokomak, it would be more practical to say they ruled the gravity points and star systems surrounding them, but vast reaches of space, particularly on the edge of their empire, remained largely unexplored, let alone integrated into the empire. One such star system gave birth to Earth.
Humans called the Tokomak Government a Government of Old Men. That is reasonably accurate; their society places great stock on older people (who are clearly blessed by the gods) and anyone over the age of 50 can expect to be part of the decision-making system. (Among other things, promotion is by time in grade, rather than merit or patronage.)
Non-Tokomak are not allowed to hold any kind of governmental office in the empire. It isn’t uncommon, however, for alien families to build up influence behind the scenes.
Earth was discovered by the Tokomak in 1200AD. As Sol lacked any gravity points, the Tokomak were largely uninterested in the human race and (after making a few cursory scans and abducting a number of humans for dissection) abandoned the system. However, several other races – particularly primitive races who had bought or stolen starships from the Tokomak – were interested. One of them abducted large numbers of humans during the 15th century and used them as soldiers on various border worlds. They proved remarkably successful, which eventually attracted the interests of other aliens, who dispatched capture missions of their own.
One such mission, in 2020, ended disastrously when their abductees, a number of American ex-military personnel, successfully captured the alien starship, along with its technology. (To be fair, the race crewing the starship was largely regarded as little more than scavengers by the other Galactics.) Being somewhat isolated from the mainstream of American society at the time (and fearing what would happen if Galactic technology was handed over to Earth without some careful forethought) the former abductees recruited family and friends, then eventually laid claim to Luna and founded the Solar Union. A steady dribble of Galactic-level technology was fed down to Earth, eventually helping to terminate the War on Terror and start an expansion into interplanetary space.
Humanity proved to have several advantages the scavengers lacked. They not only had a grasp of the basics of science – which allowed the mysteries of Galactic technology to be steadily unlocked – they also had an inventive frame of mind that allowed the Solar Union’s growing population to improve upon such technology. By the time the scavengers returned to Sol, the Solar Union was more than ready for them. Human colonies were scattered over the Solar System, while two interstellar colonies were rapidly established.
By the time the Tokomak realised that they had a growing problem and moved to deal with it, the human race was already quite some distance ahead of their technology (even the tech they’d never sold to anyone else.) The small squadron of starships they sent to punish the upstart human race were rapidly and completely destroyed. When word spread up the network of gravity points to their capital, their ruling powers refused to believe it until successive reports of two further military disasters followed rapidly. Eventually, faced with the prospect of revolt across their empire, they came to terms with humanity. Human independence was acknowledged, human traders were permitted to enter the empire at will and human slaves (descendents of those taken from Earth) would be repatriated. Not all of them, to be fair, wanted to go back to a home they’d never seen.
Politically, the Solar Union is a libertarian democracy composed of a number of planets, settled asteroids and colossal starships. (By the terms of the Solar Treaty, established when the Solar Union’s existence was revealed on Earth, the Solar Union asserts no power on Earth’s surface and governments on Earth are not part of the Union.) As long as each state accepts and upholds the Solar Constitution and Bill of Rights, they are permitted to remain within the Union.
Originally, the Solar Union saw itself as an individualist society. There would be no attempt to integrate vast numbers of people or entire nation-states. Given the boundless depths of interstellar space, there was infinite room for anyone who wanted to join – or even set up a homestead of their own. Later, as humans settled planets (and large human populations were discovered under alien control), the system evolved towards accepting entire settlements (as long as they followed the basic rules.)
(There are a number of different forms of government, ranging from direct democracy to religious or corporate states. As one of the key provisions of the Bill of Rights is that anyone who wants to leave can do so, even the most ‘conservative’ states are careful about not pressing their population too hard.)
Fleet – formally the Solar Navy – is charged with defending humanity and human-controlled star systems. The Solar Marine Corps provides ground support if necessary. (The Solar Treaty bans the Solar Union from raising more than 10’000 Marines, with the assumption that further troops would be supplied from Earth if necessary.)
The wars against the scavenger races brought a surprising number of aliens into humanity’s fold. While many wanted to remain on their homeworlds and escape further Tokomak (and other) interference in their affairs, others applied to join the Solar Union.