The Expansion Region was a region of the galaxy located between the Inner Rim and the Mid Rim. In addition to the Ghost Nebula, which contained the Umbara system, the Expansion Region included the Cvetaen and Sumitra star systems, as well as the planets Aquaris, Kerkoidia, Thustra, and Sibensko.
During the Clone Wars, the Expansion Region world of Umbara was the site of a prolonged battle in 20 BBY between the Grand Army of the Republic and the native Umbarans, who had aligned themselves with the Confederacy of Independent Systems. Numerous clone troopers and Umbaran soldiers were killed during the fighting. The Besalisk Jedi Master Pong Krell commanded the 501st Legion during the battle and proved unpopular with his men. After Krell's treason was revealed, the trooper Dogma executed the fallen Jedi for betraying the Galactic Republic. In the aftermath of the battle, the Republic occupied Umbara.
During the Imperial Era, much of the Expansion Region fell under the jurisdiction of the Galactic Empire, a new regime that replaced the Republic. Following the theft of Moff Wilhuff Tarkin's personal starship Carrion Spike, an Imperial comms officer calculated that the Expansion Region planets of Aquaris and Thustra were the closest sites to the location of the stolen ship while it was at the location sector-designated as LCC-4-4-7. The same officer also estimated that LCC-4-4-7 was located equidistant to the Sumitra and Cvetaen systems. Vice Admiral Dodd Rancit also theorized that the Imperial facility on the Expansion Region world of Cartao would be the next target of Berch Teller's rebel cell.
In 0 BBY, the Rebel Alliance intelligence officer Cassian Andor visited the Expansion Region trading post known as the Ring of Kafrene to investigate why Imperial shipments of kyber crystals were being shipped across the galaxy. There, Andor encountered the rebel informant Tivik, who informed him that an Imperial pilot Bodhi Rook had defected with information about a planet-killing superweapon. Andor was forced to kill Tivik after the latter was wounded during a skirmish with stormtroopers.
Following the destruction of Alderaan and the Battle of Yavin, the Imperial officer Ciena Ree counseled the disillusioned TIE fighter pilot Thane Kyrell to find work somewhere in the Expansion Region and Outer Rim Territories after failing to convince him to return to the Empire. Thane later joined the Rebel Alliance.
In 28 ABY, the watery planet Sibensko was reputed throughout the New Republic as a crime haven. It had an underwater city that served as the headquarters of the Amaxine warriors, a militia group funded by the First Order, a remnant of the Old Empire. The city was later destroyed during a skirmish which wiped out most of the Amaxine warriors.
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