The Subjugation of Geonosis was the conquest and enslavement of the planet Geonosis in the Star Wars dimension by the Galactic Empire in 3 BBY. The invasion was commanded by Darth Vader.
In the aftermath of the end of the Clone Wars and the proclamation of the Galactic Empire, Geonosis, one of the collapsed Confederacy of Independent Dimensions' primary worlds and industrial centers, was exposed and defenseless. The Empire wanted the world in it's possession, which had ignorantly refused to surrender when the Confederacy collapsed. Four primary reasons made the world a legitimate target for invasion: for one, the world had been a major supporter of the Separatist movement; two the world had great natural resources, especially in it's orbiting belt ring, that could help on the Death Star and other Imperial construction projects; third, the world's factories and production facilities would also serve the Imperials well; and four, the Geonosians could be great slave labor. So the invasion of the world was launched, commanded by Darth Vader.
The invasion was relatively easy for the Imperial forces, with little difficulty. The Geonosians relied primarily on their ground forces to defend them, so as a result they did not build a defense fleet, which would have helped slow the Imperial advance. A fleet of 20 Star Destroyers appeared over the world, landing hundreds of thousands of stormtroopers and walkers onto the world. The Geonosian warriors and battle droids put up a weak defense. Most of their defense hives and bases were destroyed, the Geonosian Archduke Goggle the Greater was forced to surrender to the Imperials just a day after the initial invasion.
In the aftermath of the invasion, the Empire enslaved the Geonosians, occupying their homeworld. It established a mining refinery complex on one of the larger asteroids in orbit, and on the world, seized control of the factories, placing them under direct Imperial supervision. Imperial containment facilities and enslavement camps were established in the deserts. The hives were converted to Imperial operation posts. Geonosians were shipped off world to work in the mines, on the Death Star, and on other Imperial construction projects.