|“||Well, it should be quieter since the planet was sterilized. No queens, no hives… Wonder what weapon they used. Would be nice to get ahold of that…||„|
|~ Doctor Aphra on the sterilization during her visit to Geonosis|
The Sterilization of Geonosis was a systematic genocide commited against the native Geonosian population of Geonosis that occured three years before the Battle of Yavin. Geonosis was sterilized by the Imperial military in an attempt to cover up any evidence of the construction of the Death Star which was built via slave labor by numerous alien species, including the Geonosians, which were sterilized shortly afterwards.
Death Star Plans
Prior to the Clone Wars, the planet of Geonosis was one of the many worlds that had secceded from the Galactic Republic and joined the Confederacy of Independent Systems during the war and the Geonosians had aligned themselves with the Separatists as well. On Geonosis, the plans for the Death Star were formed and were given to Count Dooku and taken back to Coruscant and given to Darth Sidious in order to prevent the Republic from finding out about them. Over the next three years, the plans would remain in secret as the armies of both the Republic and the Confederacy battled all across the galaxy until 19 BBY when both were dissolved in favor of the Galactic Empire.
Construction over Geonosis
Shortly after the end of the Clone Wars and the formation of the Galactic Empire, construction of the Death Star had went under way immediately. Geonosis was the first construction site for the new battle station and countless native Geonosians were enslaved and forced to work on constructing the Death Star over Geonosis. The construction went under way over Geonosis until some time before 3 BBY when the site was moved elsewhere the Geonosis was sterilized to cover up any evidence of the Death Star's existance.
Eventually at the end of the Clone Wars, Sidious and the Grand Plan was complete, the Republic had fallen and the Jedi Order was in ruins and the empire had ushered in a new age with the galaxy ruled by the Sith. Construction of the Death Star was first overseen by Vice Admiral Dood Rancit and then by Imperial Moff Wilhuff Tarkin but the site was moved to another location. To prevent any evidence from being found, the Imperial Military attacked Geonosis by sterilizing the entire planet with canisters of poison gas, killing 100 billion Geonosians and nearly wiping out the entire population.
With a death toll of 100 billion, the Sterilization of Geonosis was the largest single act of mass murder ever carried out by the Galactic Empire.
In the aftermath of the sterilization, Geonosis lay in ruins and was added to the list of countless planets that fell victim to the Galactic Empire and their many genocides that they had committed. Nearly all of the native Geonosians were wiped out, but there were still survivors. The only known recorded and named survivor was the Geonosian Queen Karine the Great who hid in an underground lair merging B1 Battle Droids with Geonosian DNA to create her own breed of Geonosians and to repopulate the planet. She was eventually found out and discovered by the Empire during a mission to Geonosis conducted by Darth Vader. Sometime before the Battle of Scarif, the Ghost Crew of the rebellion had traveled to Geonosis on a mission and located Saw Gerrera as well as another Geonosian known as Klik-Klak who had a small group of battle droids gaurding him and revealed the Death Star plans to the rebels.
In the Legends continuity, Geonosis had established an isolationist policy sometime after the Galactic Civil War, revealing that there's still a form of government and other survivors on Geonosis and that the Geonosian species had survived. It is currently unknown if anything similar happened in the Disney canon, where it is implied that Klik-Klak and the young Queen Karina may really have been the only survivors of the species.