Here's an excerpt from the WIP article on the subject, which I think may answer some questions without my addressing them directly in a spoilerific fashion; I'm not going to spoiler tag it because I don't think backstory stuff really constitutes spoilers, and the spoiler tags don't play well with the forum dark mode, but if you'd rather not see such things, then don't read it!
CONSIDER THIS A SPOILER TAG 
(Some of the references may be confusing as this is missing the section describing the geography and biome of Seren, but I think it's mostly comprehensible.)
History of the Seren Occupation
In June of 2139, with Umiak forces bearing down on Seren from two sides and threatening to cut off the escape routes, the Loroi fleets defending the system withdrew, leaving the evacuation incomplete and stranding some 50 million Loroi on the planet, mostly civilians. Included among those trapped were a few military ground units supervising the evacuation, and a number of children. Despite priority given to children and pregnant females during the evacuation, a few failed to make it off the planet in time, the largest group of these being diral students who had been in the wild and out of contact. There were no males among the Loroi captives.
With the planetary government already having fled, there was no formal surrender or centralized command for resistance. There was only sporadic fighting from the minimal Loroi military ground presence as Umiak invasion forces occupied the major cities. Some of these Loroi troops were killed during the fighting, a few surrendered, and the rest fled into the countryside. The Umiak quickly secured their control of all the major population centers and confined the Loroi captives into cordoned-off sections, which would eventually be transformed into huge prison compounds. In short order, the Umiak put the Loroi captives to work, mainly in resource extraction operations (Seren being a mineral rich world). The work regimen was typically harsh for planets under Umiak control, and Loroi of all ages were required to work. Over the next six years, many Loroi internees would die from exhaustion or malnutrition. Within the first year of occupation, the Umiak liquidated most of the military Loroi prisoners, recognizing that they could not really be securely confined.
Seren's geography, including the mineral "forests" and network of caverns created by the native
nilesein lichenoid colonies, provided excellent cover for partisan bases outside of the urban areas, even against Umiak ground-penetrating radar and infrared sensors. Low-level resistance began from day one by the Loroi forces dispersed in the foothills and caverns, including the remnants of the garrison units and even a few diral bands that had not returned to the population centers to be captured. The resistance forces included small numbers of Teidar and Mizol, who could conduct sabotage operations right under the very noses of the occupiers, evade capture, and blend in among the among the civilian prisoners despite extensive electronic monitoring. Seren's extensive shipyard facilities, captured more or less intact by the Umiak, were a particular focus of sabotage attempts. In the early stages of the occupation, these resistance efforts were entirely local, as there was no central control or any contact with the outside Loroi chain of command.
During the whole period of the occupation, throughout the Steppes, Loroi prisoners were routinely made the subjects of unrestrained medical experiments by the Umiak, who were very eager to learn how Loroi telepathy worked, and hoped that large-scale experiments could reveal what smaller scale examinations of earlier captives had not. These experiments met with only limited success in terms of Umiak knowledge of telepathy, and the program resulted in one of the most damaging incidents of the Seren occupation to that point, when a group of young Loroi research subjects who were being studied for operant psychokinetic abilities rebelled and destroyed the entire research facility and then rampaged through the nearby internment compounds, freeing fellow prisoners. Most of the escapees were eventually recaptured, as they had all been tagged with various tracking measures, but a few remained at large, and are presumed to have joined the Loroi partisan forces in the countryside.
This incident brought into sharp focus for the local Umiak commanders what had been a slow realization: that the Loroi population of Seren could not be effectively pacified in anything like a predictable short term. It was at this time, two years into the occupation, that the directive was issued to begin the liquidation of the remaining Loroi captives throughout the Steppes region.
On Seren, Loroi partisans learned of this directive even before the mass executions started, and the word spread among the disparate resistance groups to simultaneously and hurriedly go forward with any and all planned operations that they had within their capabilities. These included direct attacks on the interment compounds and Umiak resourcing operations. The most dramatic of these sabotage efforts succeeded in severing the connection of the large orbital elevator from Leinazal (the most populous Seren city and the center of its industrial heartland) to the shipyard complex, resulting in its partial collapse. Quick and effective Umiak countermeasures prevented the complete collapse of the elevator, but the partial collapse severely damaged the lower portion of the elevator and destroyed most of the industrial quarter of Leinazal, plunging the entire region into outright revolt, and rendering the elevator useless.
The Umiak accelerated liquidation efforts and dealt with the Leinazal uprising through orbital strikes, destroying most of what remained of the city. The escape of large numbers of prisoners afforded a short term tactical advantage to the Umiak occupation forces, as they were easily tracked and could be used as bait to ambush units of the Loroi resistance as they attempted to rescue the escapees. However, despite the successful extermination of some 90% of the remaining Loroi population of Seren and the worst losses of the occupation for the Loroi resistance forces, at the end of this purge the Umiak held no more prisoners on Seren, yet more than half a million partisans were now dispersed throughout the wilds. While the Umiak occupation forces had been released from almost any restraint in the hunting down and extermination of the remaining Loroi, the surviving Loroi partisans had similarly been released from any concern over reprisals against captive Loroi, and all surviving Loroi were now a part of the resistance effort, whether civilian or military, adult or child.
Over the last three years of the Umiak occupation of Seren, a bitter guerilla war was waged between the Umiak and the surviving Loroi. Though the Loroi resistance fighters were steadily decreased in number by Umiak operations, Loroi resistance activities brought the Umiak resourcing operations on Seren effectively to a halt. Individual Loroi partisan groups and even individuals became known and feared by the Umiak occupation forces, including the Leinazal resistance group calling themselves "The Smelter" (after the name of the destroyed industrial district of their city), and the enigmatic lone operator that became infamous to the Umiak as "The Forge Child." The Loroi resistance forces became better organized respite their losses, and Umiak casualties mounted with very little to show for their efforts.
Seren was liberated by the Loroi in 2145 during the Semoset offensive, when Sunfall's fleets pushed the Umiak lines back across the Steppes. The occupation had lasted 6 years, and in that time roughly 49 million Loroi had been exterminated by the Umiak. Perhaps surprisingly, the Umiak evacuated Seren almost completely and did very little to destroy the remaining surface or orbital infrastructure; it seems likely that they had expected to reoccupy Seren in the near term. But they did leave some terrifyingly altered and boobytrapped former Loroi prisoners. The Loroi liberation forces quickly realized the necessity to quarantine the 600,000 survivors on Seren pending processing to make sure that they had not been tampered with by the Umiak (including, sadly, in some of the same internment facilities that had been used by the Umiak). Some of the resistance groups were so dispersed and well-hidden that it took more than a year to contact them and bring them back into the fold of Loroi civilization. But the barbarity of the fighting had left its mark on the survivors, and many had to be institutionalized, and in a few extreme cases, euthanized.
