In the beginning of recorded galactic history, Core was formed. A republic to span the stars and rule them, and all their inhabitants. None knew why humans populated planets across the galaxy. But Core did not trouble itself with such minor details in it's quest for galactic “peace and order”. It spread to planets, making contact with the sentient inhabitants.
Offering them the chance to join the republic, to strive with them for a better future. Many were swayed by these types of statements. But some...some could not see themselves giving up the freedom of their world to what they deemed a power-hungry monster. Some resisted. And such resistance was met with Core's military might. Many worlds broke at such displays of power. But some fought.
Rebellion brought forth the full fury of Core, as it's thirst for new territory was unquenchable. Planets were forcefully subjugated, resistances smashed, the people “re-educated” in camps. The knowledge of the methods used by Core's military under the direction of the bureaucrats never reached the citizens of Core. At least not the way it actually happened.
The news displayed videos of victory over rebel forces. The citizens were content, caring little for the small numbers lost putting down such “rebellions”. They all knew of course that any worlds with humans on them were part of Core. Part of the whole. They just split off from Core, and needed to be brought back, to see how wonderful it was being a citizen of Core.
Then Core encountered a world more advanced than they knew, almost to the level of Core. The Te'alnarn chose to fight. The war ravaged Te'aln, and killed millions on both sides. The beast which was Core took notice of the small yet stubborn planet.
Large scale losses are hard to hide. The cover up was daunting at best. But it was done, as it always was, though the challenge became more and more difficult. The forces of Te'aln were successfully holding the invaders at bay. Core recognized the need for a new weapon.
Scientists were put to work devising this new weapon. It was to be cheap to manufacture. Silent communication, no need for resupply, ruthless and efficient. It would follow orders unquestioning, all the way to death. The Janetul.
But there were problems. The Janetul could not adapt to new developments on the battlefield. Could not counter new threats. The Te'alnarns learned this weakness, and exploited it to great effect.
Core, too, saw the weakness. The scientists fixed their creations. They made them sentient. Gave them free will, while still programming undying loyalty to Core. Te'aln was wiped clean in a matter of weeks.
Some of the Janetul began to see how they were used. Loyalties were broken. A large force of Janetul were sent to exterminate the small problematic number. But the scientists forgot to remove a base loyalty in their genetic tampering. Loyalty to race.
The Janetul were made with no need to breathe, so that poison gas could not be used on them. Vacuum also had no effect. The fleet was taken in hours. Contact with Core was severed.
Two months later, the war began. Core collapsed a month later when the Janetul warped over Core Prime.
The Janetul used kinetic energy weapons, slamming bars of uranium moving at 0.3 cee into the central government world. The outlying military, the last cohesive force left, quickly took control of the situation as Core Prime, the politicians, and the main military leaders were reduced to dust in space.
Junior officers quickly began to piece together what had happened, what their government had done. And changes were made.
The new government wasn't just militaristic. It was the military. Martial Law was declared on surviving Core worlds, with orders to evacuate all planets given. The fleet grew, until a young lieutenant named the fleet. Redemption.
It became the closest thing the survivors of Core had to a planet. Constantly moving to avoid annihilation, while making trying to save those planets that did not know what existed out there. Did not know of the enemy out there, eager for revenge against it's creators.
A system was devised for untouched worlds. A small detachment from Redemption would be sent to the planet. Operatives were created, test tube babies with memories and ideals programmed into them genetically, set to be activated by a coded transmission which would be received by a receiver wired into their brains.
They were sent down to the planet's surface as children, some being “found” and placed in orphanages, others being sent with “parents”; volunteer civilians who would have their memories written over after the planet was studied Individuals who could teach the operative ideals and values as they grew.
Eventually, the Janetul would find the planet. They always did, somehow. They would attack, dropping to the surface to begin their harvest, turning humans and other organics into food, torturing them for entertainment as near as could be gathered. Revenge for how they were made.
Operatives would be activated. Dormant nanotech would activate, strengthening muscle, enhancing reflexes and senses. Weapons and armor would be dropped to the surface, along with military personnel. Evacuation would begin. Operatives were assigned with this task, assessing those that they knew of potential value and selecting who would go. Then in a matter of a couple hours it would be over.
The detachment would withdraw.
A chosen operative would be tasked with removing anything from the location that was of value to the Janetul. Six 200 kilometer asteroids, moving at over ninety kilometers per second were used to accomplish this task, fired through tunnels which opened around the planet.
With a code, a palm scan, and the push of a button, the world would cease to be habitable to even the Janetul.
It was always an act of mercy, killing a planet.
The Janetul prefer live captives.