General History

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Approximately 2,000 years ago humans developed jump travel and proliferated among the stars, far more aggressive in colonization than the limited alien species that they encountered (of which many seemed content with staying in their own systems). Almost 1,500 years ago they eventually encountered another group of humans that called themselves the Altarians. The Altarians had controlled their region for the past 400 years as an empire (the Imperium). A vast war quickly broke out with the Atlarians victorious.

Being genetically the same species as the humans of Sol, the Altarians underwent a period of broad social engineering along with expanding Imperial families to include them. Their cultures and identities merged into what is called Humanity today and what followed was a period of long peace. Things were not to last however. While alien species had the rights of Imperium citizens, they were treated as minorities. Exceedingly few were ever put into positions of power within the Imperium. Humans from the old region of Sol began to foment dissent, calling to aliens to help them form a republic.

Some aliens heeded the call, while others stayed neutral (and fewer species even sided with the Imperium). The 100 year war broke out. A civil war that eventually split the Imperium from the core worlds of its empire from those in the outer rim. Twenty years ago a truce was called. The outer rim region became the Federation, a republic of systems with leadership and military made up of several sentient species. While humans are certainly the majority of the Federation, more aliens make up the ranks of its military and government than what is seen in the Imperium.

Current Events:
Known explored space is approximately 1,500 parsecs across, with almost two thirds of it under dominion of the Imperium. The remaining outer third is under control of the newly established Federation. In all there are over 20,000 known habitable worlds in this vast area of known space. Humanity, or Humans, are not alone. There are a handful of other major alien races that lay claim to sector regions on the Imperium’s periphery, and a multitude of other minor races that may only claim two or three planets under their respective domains. The only known race that has larger number of systems under their control are the Rezolians, and the extent of their empire is unknown.

With the 100 year war done, most are happy to see peace again. Yet 20 years is not a long time. Some are still bitter about the wane or increase of the respective galactic powers in their system. A few Federation planets look negatively on some alien species that sat out the war (but reaped the benefits). Some Imperium planets pine for more regional representation, rather than being dictated to by a power afar. And some wonder if the war was stopped due to a willing agreement from both sides, or was it the potential threat of the Rezolians, an enemy of all, which forced each side to capitulate.

Humanity and the Great Mystery:
Archaeological research has shown that in approximately 5,000 BC humans from Sol were removed and stocked among key planets within the cosmos likely leading to the establishment of the Altarian Empire. This has become a well established fact. Who were these beings and why did they deem it necessary to plant mankind among the stars? Even more mysterious, it appears that some alien races have genetic ties to animals on Earth, indicating that far ancestors of these young alien races may have been uplifted for some unknown purpose.

[Note: Much of this is lifted from a campaign primer explaining the Traveller universe. No claim over any of this.]