During the Mage Wars they were known as the Rethosin Empire and collaborated heavily with the Marcon Alliance, despite different ideologies. They engaged in numerous space-faring conflicts with the Runarins and the M'KHarens, both of whom eventually conquered much of the empire's territory in space, leading the Rethosins to establish off-world colonies and refugee sites on Flat worlds and to develop inter-dimensional travel magic (uncommon for a largely space-faring, technological society).
During the Second Chaotic Period, the Rethosins joined Eieber and were part of all three early iterations of the Alliance, though as vocal opponents of many Alliance concepts, they may have contributed sigificantly to some of the earlier collapses. Notably: the idea of a Commonwealth was first proposed during the Ministry of Earth, but was opposed most vocally and actively by the Rethosins.
By the early Golden Age, the Rethosins had become largely withdrawn, and while they maintained membership in the Alliance, they took a far less active role. During the Ninety-nine-years war, they were among the most hostile. It was in the mid Golden Age that they typically referred to themselves as the Rethosin Alliance, as they attempted to garner allies for new Mage Wars.
With the dawn of the Second Age, the Rethosins had settled down somewhat and become less outwardly hostile. The society grew more closed, and while they continued to trade with the outside world, it became clear they had no interest in belonging to the rest of civilization.
During the Kamian Succession Wars, the Rethosins claimed to remain neutral, but ample evidence was gathered that they had secretly been supplying the Kamians with raw materials and other resources. Because the Rethosins were still officially members of the Alliance, they could not be declared enemies in the war.
Proceedings began to have the Rethosins formally removed from the Alliance, but this could not be completed by the time the war ended. The procedings ground to a halt, and the Rethosins remained members of the Alliance, though barely.
Darksesis is the name of a Rethosin penal colony. It is a small moon orbiting a black hole orbiting a second black hole. Due to the complex gravitational interactions, it is believed to be inescapable. The Rethosins exile all of their political prisoners there.