Fought towards the end of the Clone Wars in 19 BBY, the siege at Onderon was an attack launched as part of the Outer Rim Sieges campaign by the Confederacy of Independent Systems. An assault on the Inner Rim planet Onderon, the world had previously been occupied by the Confederacy, but the Galactic Republic and Onderon rebels wrestled control of Onderon from the Separatists in 20 BBY during the Onderonian Civil War. Saw Gerrera, a veteran of the still-recent Civil War, fought for the Republic during the siege.
When the Clone Wars between the Galactic Republic and Confederacy of Independent Systems began in 22 BBY, King Ramsis Dendup of the Inner Rim planet Onderon decided to remain neutral on the belief that both sides were corrupt and that such a choice would spare Onderon from the horrors of war. In reaction, the CIS invaded the world by covertly supporting a pro-Separatist coup, which brought Separatist puppet King Sanjay Rash to power. With the puppet king "inviting" the Confederacy military to Onderon, the Separatists secured a firm foothold over Onderon through an occupation. Although Onderon's representative in the Separatist Senate, Mina Bonteri, firmly believed in the Separatist cause, the Confederacy's violation of Onderonian sovereignty inspired a resistance movement of citizens under siblings Steela and Saw Gerrera. The ensuing Onderonian Civil War would last from 22 BBY to 20 BBY. In that latter year, the Onderon rebels formally approached the Jedi High Council for help in overthrowing Rash.
When the Confederacy of Independent Systems occupied Onderon under a puppet king, a civilian insurgency emerged to retake the planet.
Unable to directly interfere on a planet that had chosen to align with the CIS, as the Republic recognized Rash's rule, Jedi General Anakin Skywalker proposed a covert operation to train and support the local insurgency. Although Steela gave her life during the battle, the Separatists were ultimately ousted from Onderon, with Rash being executed for his failure by General Kalani on the order of Confederate Head of State Count Dooku. As Mina's son, Lux Bonteri, who had lost faith in the Separatist cause after Dooku had his mother killed, promised during Steela's funeral, Onderon then returned to the Republic. Lux served as its senator while Dendup returned to the throne. The people of Onderon remained loyal to the Republic for the rest of the war.
In 19 BBY, towards the end of the Clone Wars, General Grievous launched a major Separatist offensive during the Outer Rim Sieges campaign. As part of the sieges, the Confederacy military besieged the recently-liberated Onderon, turning it into a battleground once more. Just as he had in the Civil War, Gerrera fought on behalf of the Republic during the siege. He also began to use Skywalker's Fulcrum frequency to keep in contact with the Jedi. The battle was dubbed the "siege at Onderon." During the Battle of Yerbana, when former Jedi Padawan Ahsoka Tano and Mandalorian Bo-Katan Kryze contacted the Republic using the Fulcrum frequency, Skywalker and fellow Jedi General Obi-Wan Kenobi initially thought Gerrera was trying to contact them, with the latter speculating that Gerrera's efforts had taken a negative turn. However, Admiral Wullf Yularen informed the Jedi it was not Gerrera contacting them, and the two soon learned that it was instead Tano and Kryze.
The Clone Wars came to an end when Skywalker, as the newly-christened Sith apprentice Darth Vader, wiped out the Executive Separatist Council on the planet Mustafar in the Outer Rim Territories. Vader also sent out a shutdown signal to the Confederacy military, leaving the Separatist Droid Army to cease its ongoing attacks and stop in its tracks. However, the end of the war did not mark the end of Gerrera's troubles; the Republic was reformed into the Galactic Empire by Supreme Chancellor Sheev Palpatine, who was secretly the Sith Lord Darth Sidious. As Palpatine, Sidious also sent out Order 66 to the clone troopers who served alongside the Jedi, forcing the clones to wipe out their own commanding officers because of the behavioral modification biochips installed in their brains. Gerrera recognized that Palpatine had unlimited control over the clones and believed a new civil war was imminent.
In the aftermath of the Clone Wars, Saw Gerrera encountered Clone Force 99 and urged them to rethink their loyalties.
Despite their work with the Republic during the war, Gerrera and his remaining rebel fighters refused to fight for the new regime. As such, they were dubbed enemies of the state in the opening days of the Imperial Era. Even though Gerrera had been promised that Onderon would be free after the war, the Empire moved to annex the world, and so Gerrera reformed the Onderon rebels into a rebel cell named the Partisans and protected a number of civilians. His fighters soon captured an elite team of clones—Clone Force 99, otherwise known as the "Bad Batch"—that had been dispatched by Imperial Admiral Wilhuff Tarkin on the claim that they would find Separatist insurgents. Gerrera urged the clones to resist the new Imperial government before letting them go. Declaring their own war against the Empire, Gerrera and his Partisans waged a brutal insurgency for the future of Onderon but ultimately abandoned the world.
The siege at Onderon was first mentioned in "Old Friends Not Forgotten," the ninth episode of the seventh and final season of the animated series Star Wars: The Clone Wars, released on April 17, 2020.
- Star Wars: Timelines