The Corellian Treaty was an accord that created the Alliance to Restore the Republic. Signed by the leaders of anti-Imperial resistance groups on Alderaan, Corellia, and Chandrila, the treaty formally declared war on the Empire. Though the meeting to create the treaty was arranged by Galen Marek, this proved to be a deception by his former master, Darth Vader, who raided the meeting with the Stormtrooper Corps and captured the three senators. Had Galen not survived his confrontation with his former master, the Empire would have effectively ended the Rebellion before it even began.
The leaders of a "Rebel Alliance" meet.
Garm Bel Iblis, having consolidated the resistance forces on Corellia under one command structure, called Bail Prestor Organa of Alderaan and Mon Mothma of Chandrila, who had discussed potential revolution at the Cantham House Meetings, to Corellia for a new series of discussions. These Corellian System Meetings proved more successful, and the three resistance leaders drafted the Corellian Treaty as a codification of their common ideals and goals. Bel Iblis, Organa, and Mothma's signing of the treaty formalized the relationship between the Corellian, Alderaanian and Chandrilan resistance forces, respectively, from a loose coalition to an organized rebellion.
The treaty itself provided a command structure for the Alliance intended to allow each force to govern itself while providing a strong centralized component to coordinate all efforts. It organized the civil aspects such as diplomacy, transport and supply into one tree, bundled all military operations into another, and placed the Commander-in-Chief and Advisory Council at the top. Organa told Bel Iblis and Mothma that he could fund a rebellion, while Bel Iblis would provide ships for its fleet, and Mothma would help provide soldiers.
The treaty, having been suggested by Darth Vader to Marek, was actually a ploy by Emperor Palpatine to lure all of his enemies into a single place to capture them. Just as Bail Organa declared the treaty finalized, Imperial forces suddenly swarmed the building. As Stormtroopers burst into the meeting room and killed all of the guards, Bail ordered PROXY to cut Leia's transmission, concealing her involvement.
As PROXY did so, Darth Vader marched into the room, commanding the troopers to capture the Rebels alive for personal execution by the Emperor. Kota immediately drew his lightsaber and charged at Vader, but the Sith Lord easily incapacitated him with a Force grip, tossing him aside. As the Rebels were rounded up by the stormtroopers, Vader approached Marek and complimented him on his performance, revealing to the shocked Rebels the "Jedi's" position as his apprentice, before telekinetically smashing the stone table in the room into Marek.
Darth Vader on Corellia.
Marek was hurled out of the meeting room onto the snow-covered cliff ledge surrounding the site. As he attempted to regain his feet, he angrily questioned Vader regarding his presence, as he had agreed to stay away. The Sith Lord stated that he had lied, as he had done so from the very beginning. Realizing the very beginning referred to the beginning of his apprenticeship under Vader, Marek now knew that Vader had no intention of destroying the Emperor—not with him, anyway. Vader grasped Marek with the Force and hurled him over the cliff, though Marek managed to grab hold of the edge. Marek looked up at the advancing Vader, calmly declaring that Vader would never be free without him.
As Vader raised his lightsaber to finish Marek, he was suddenly attacked from behind by what appeared to be Obi-Wan Kenobi, Vader's former Jedi Master. Briefly caught off guard, Vader was forced back a step. However, he quickly rallied, blasting Kenobi back with a Force push and impaling the Jedi before he could recover. "Kenobi" suddenly dematerialized, revealing himself to be PROXY utilizing his Kenobi combat module. The holodroid fell to the ground, his last word being a call to his master, distorted by his failing computers. Vader kicked the droid lightly to check if he was subdued, and satisfied that he was, turned back to the cliff.
Vader is attacked by "Obi-Wan Kenobi."
However, Marek was gone, having lost his grip and fallen while Vader had dealt with PROXY. Vader deactivated his lightsaber and rejoined the troopers within. However, Marek had survived his fall, and was rescued by Juno Eclipse. Resolving to pursue Vader and rescue the Rebels, Marek used the Force to locate their ultimate destination; the Death Star.
The three senators and Kota were taken before the Emperor himself, who gloatingly declared that they would be tortured, interrogated, and ultimately, executed. However, before Palpatine could dispose of the Rebels, Marek arrived and confronted Vader and Palpatine. The Jedi almost killed Vader, but lost his life confronting the Emperor after nearly killing him as well. Thus, he still bought the time for the Rebels needed to escape.
Later, after Marek's death at the hands of Darth Sidious, the Anti-Imperial Senators returned to Corellia and revived PROXY. Afterwards, Leia met with Bail Organa, Mon Mothma, Garm Bel Iblis, Rahm Kota, Juno Eclipse, and PROXY on Kashyyyk, forming the Rebel Alliance. Leia picked a symbol for the Alliance, the symbol of the Marek family, in a tribute to Galen Marek, his family and his victories against the Empire, and so began the Galactic Civil War.
The treaty inspired dozens, then hundreds, then thousands of resistance cells across the galaxy to join the Alliance, such as Sian Tevv and the Sullustans and Jenssar SoBilles and his Duro fighters. Several organizations became part of the Rebel Alliance, including Kota's Militia and most of the surviving Separatist holdouts. In which they soon established Sanctuary Base on Dantooine, as the first command center of the Rebel Alliance.
One of the stipulations of the Corellian Treaty was that, upon the death, resignation, or overthrow of Palpatine, the position of Chief of State would cease to exist. Instead, a Constitutional Convention was required to be called, to debate the form of the restored Galactic Republic.
The Corellian Treaty, the founding document of the Rebel Alliance, was originally introduced in the roleplaying book The Rebel Alliance Sourcebook (1990) and was subsequently mentioned in numerous other sources. However, the circumstances resulting in the signing of the treaty and the birth of the Alliance were not fully established until the release of the 2008 multimedia project Star Wars: The Force Unleashed. A number of implied and stated details were changed for the purposes of The Force Unleashed, such as the motivation of the founders.