Spelljammer Kingdom Hearts
Centuries ago, there was only one planet in this system that supported life. Humans, elves, gnomes, dwarves, halflings, even goblinoids and orcs, all on the same planet. Eventually, an industrial revolution started. Gnomes made advancements in clockwork, dwarves discovered coal and developed gunpowder. It didn't take long for them to start creating new technologies that surpassed anything else ever seen on this planet. Dwarven paladins took up arms in steam powered suits of armor with shoulder mounted cannons and huge, powerful hammers. Gnomes crafted analytical engines that made warcraft far different than it had ever been. An Engine's power to make predictions in matters of strategy and statistics gave the new subterranean superpower an ever growing edge over the world. As peaceful as the dwarves are in general, they provided a safe haven for halflings and humans that had never been provided for before.
It wasn't long before they were challenged. Hobgoblins have long had powerful military traditions, but most of the clans were relatively evenly matched, locked in a long standing cold war between multiple parties. The new technologies, however, gave an incredible advantage to the first clan to understand them. Between the goblin's fascination with explosions, alchemy, and tinkering, and the hobgoblin's mind for science and strategy, one clan caught on to the advances made by the dwarves and the gnomes, and became another superpower, almost overnight.
The decades of pollution and poisoning the planet had already set many parties, mostly elves and fae and plants, on edge. When the war started, that was the last straw. The elves used their mastery of magic, and the fae used their mastery of nature, to grow huge liveship arks. Once they were completed, they left. Eventually, after months of flying through the expanse between the planets, they discovered another planet that could support life. It didn't take long for their considerable masteries to terraform the planet into a lush, green forest world. The fae and the elves each established their own kingdoms, the elves putting much of their focus on arcane magics, while the fae put their eggs in the druidic basket.
Eventually, the hobgoblins took the step that the dwarves were not prepared to take: they learned how to follow the elves into space, and they steered some asteroids from the system's belt into the planet. While their primary targets were the dwarven strongholds, they just weren't aware of the true devestation such mass driver weapons would have, and they covered the planet with dust and soot, forever altering the ecosystem and starting a new ice age. Most of the dwarves were killed in the hobgoblins' onslaught, but there was a large enough percentage of them that had dug so deeply, they barely felt it when the planet was struck. As a response, they sent half their kingdom to space, to make new homes in asteroids. They took to space travel pretty easily, actually, as they were so used to tight closed spaces undeground, adapting to the same conditions in asteroid mines wasn't a huge leap.
The last force to consider in the Binar system is the pirate alliance. The elves that took to the industrial revolution when it started eventually became the drow. The deep dwarves were affected by ther exposure to the radiations found so deep in the earth, and developed psionic powers. Hobgoblins are so antagonistic against magic that when there were those born with powers that seemed magical in nature, but were truly psionic, they exiled them. As infants, that should have killed them all, but one survived to adulthood, then began to rescue those that came after him. When he created a new clan of hobgoblins capable of things the others couldn't explain or compete with, he made them all targets. Instead of trying to fight against the dozens of clans that were now looking for the blood of him and his kin, he brought them to hide in the asteroid belt. In the end, there are many races that have followed the elves in their exodus. Finding no other planet to call home, they found the resource rich asteroid belt to be a great place to hide. Many of them became pirates, as the hobgoblins have now transferred most of their attention towards the pristine planet across the stystem and the elves have gathered to its defense. The pirates prey upon the supply lines both sides have to keep open to their defenses. It's a dangerous game, but in their desperation and cooperation, the pirates themselves have become a force to be reckoned with.