The Tatooine-Geonosis war (also known as the Arkanis War) was a major conflict that took place between the Tatooine of Fourth League Kingdom and the Imperial Geonosia (formed from the Duchy of Geonosis , which was showing an imperial attitude).
The war lasted 40 years, and claimed the lives of over 200 Million beings on both sides. The war was supposedly localized to the Arkanis sector, but spread as as far away from Tatooine/Geonosis as Ryloth .
The war began with the assassination of Prince Jerepar , the brother of Barraki Carapar V , in the E'Y-Akh Desert , supposedly by the Geonosian government. Subsequently, an ultimatum was issued by the Barraki to Geonosis, forcing them to agree to conditions. When Geonosis refused, a short battle took place between the Geonosians and the Barraki's forces. When victory went to Carapar V, he believed the issue was resolved, when the Geonosians invaded Rodia . This kick-started a full scale war.
The Geonosians eventually seized the planet Tatooine using Solar Siege Engines , which concentrated massive amounts of solar heat onto the planet's surface. The Geonosians would have nearly won the war, were it not for the development of a massive nuclear weapon, the Kork-Rhek , by the Barraki's scientists. Kork-Rhek was dropped on the Glomilyn Hive on Geonosis, killing the Geonosian Queen, and prompting the Geonosians to surrender. The Archduke was taken into captivity.
When the celestials heard news of the Archduke's capture, they called for him to be sent to The Pit on Ghalon Mahri, but Carapar V had him hanged before the news reached him. After the war, the Duchy of Geonosis was dissolved.
In the 40 years of war, over 200 million beings were killed, most of them Rakatan or Geonosian soldiers, but thousands of Twi'Leks and Rodians were killed in the battles that took place on their homeworlds.