Astral Saga: Stars of Strife
Unbeknownst to the rest of the galaxy, and to themselves, the Kroll are actually a very ancient race, dating back to the Lost Ages, during which they served under the Haluud. They were tasked with the construction of an artifact world that could draw upon the power of the Eldritch Realms.
When the Crownbearers went into hiding, and the Haluud went with them, the Kroll were left without masters. At that time, black stone beings from another realm, the Kholek-amn-Atan, set their eyes upon the artifact world. They took over the world, declaring themselves the new masters of the Kroll, and enslaved them.
The Kroll were bred to be subservient, and hard workers. Under the oppressive reign of these immortal constructs of black stone, the Kroll labored for a hundred thousand years.
Eventually, an expeditionary force from the Minon Confederacy found the artifact world. Although the Kholek ruled the world without opposition, they were relatively few in number. As such, they were unable to prevent the Minon Confederacy from liberating large quantities of their servants. However, the Minon Confederacy could not liberate them all, nor could they hope to take the artifact world from the Kholek.
To this day, many of the Kroll believe that they will someday have the power to reclaim the artifact world, and drive off the Khadrok.
The Kholek, however, have no intention of reclaiming the slaves that were liberated. They still control the artifact world, and can breed more Kroll slaves to labor for them. The affairs of simple mortals are beneath their consideration.