Scattered Worlds race which flourished c. 500 million BCE.
The Children of Lavarren were descended ( via Pylistroph Seed Vessel) from the Evellan. Physically, they were tall and willowy, and had rudimentary wings that allowed them to glide in Lavarren's low gravity. They were long-lived, with a juvenile phase that lasted about six to eight Human centuries, and and adulthood that could easily span ten thousand years.
Over the course of about six hundred millennia, using simple lightsail technology and a primitive form of ultrawave, the Children of Lavarren forged a union of roughly three hundred worlds across a distance of about two hundred parsecs along one Galactic Arm. They sent our exploration parties across the Galaxy.
When a long-distance exploration team from Lavarren penetrated the Gathered Worlds, the Children of Lavarren attracted the attention of Garadhros. Slowly, carefully, agents of Garadhros moved through the Lavarren union sowing the seeds of dissent and war. The Children of Lavarren, who until now had been peaceful, discovered war -- and soon the union was torn by strife.
At last, researchers on Lavarren itself developed a doomsday device: a method of triggering the simultaneous supernovae of sixteen key stars throughout the union, thereby flooding space with hard radiation that would render the entire arm of the Galaxy uninhabitable.
The crisis raised enormous moral conflicts among the ranks of the newly-formed Galactic Riders. The Riders finally came to realize that the only way to prevent the Children of Lavarren from self-destruction was to take away their freedom, and so they focussed their attention on evacuating innocent sapients, and (in the last throes) saving and preserving works of art.
In the end, of course, the doomsday device was used. And so the Children on Lavarren passed away in suicide, while the Scattered Worlds, Hlutr and Daamin and Riders alike, watched in sorrow.