It all began in the year 2 BBY (Sullustan Year 8,494) when Sin Suub, Chairman of the SoroSuub Corporation illegally took over control of Sullust in the name of SoroSuub, and announced that, as SoroSuub was a firm supporter of the Empire, Sullust itself also became one. Many Sullustans, traditionally loyal to SoroSuub, were furious at this decision.
The angry Sullustans found a leader on politician Sian Tevv, who had chosen not to join the Rebel Alliance. Nevertheless, Tevv managed the growing Sullustan resistance movement against the Empire. They staged different attacks against SoroSuub's assets, becoming so dangerous that SoroSuub had to create the Sullustan Home Guard to protect themselves against the resistance movement.
However, the Home Guard was composed only by native Sullustans, many of whom disagreed with SoroSuub's pro-Imperial stance; thus, the Home Guard was not effective when dealing with the resistance movement. This, added by the courage and dedication of many resistance fighters like Nien Nunb, became a menace for SoroSuub.
SoroSuub was forced to call for Imperial reinforcements at least in one occasion under attack of the resistance movement. The opportune arrival of an Imperial-class destroyer changed the tide of that battle, turning a sure victory for the resistance movement into a sound defeat, where Nunb lost his ship.
At this stage, a great amount of individual anti-Imperial Sullustans were joining actively the Rebel Alliance and not the Sullustan resistance movement (including some important desertions, like Nunb's). However, Tevv was firm in his decision: The Sullustan resistance movement would not join the Alliance at that moment, probably because he feared Imperial retribution.
Tevv's resistance movement was strong enough to take control of Sullust shortly before 0 BBY. At this stage, SoroSuub understood that neither the Empire nor themselves could fight any longer the piracy and sabotage of the resistance movement. SoroSuub finally sided with the Rebellion, but Sullust did not for a little longer.
The Empire, as part of Operation Strike Fear, was planning a possible invasion of Sullust. They captured Sullustan technical staff and leaders and were transporting them to Coruscant for probable interrogation, torture and servitude. Hoping to persuade the Sullustans to join the Alliance, the Rebels mounted a rescue operation.
After the rescue Sullust agreed to enter negotiations with the Alliance. A diplomatic meeting near Sullust was interrupted by the arrival of the Imperial-class Star Destroyer Invincible. The Rebel pilots, Hamo Blastwell and Keyan Farlander, flying R-22 Spearheads, held off the Imperial fighters until the meeting was concluded and all ships fled into hyperspace. The Invincible's attack, however, turned out to be merely a diversion. While the meeting was taking place, stormtroopers kidnapped the Sullustan leader Sian Tevv. Farlander and Blastwell were called into action again to disable the shuttle that bore him to the Invincible and hold off Imperial fighters until a Rebel shuttle conducted a boarding operation and escaped into hyperspace.
After the Rebel's recent assistance, Sullust agreed to become an ally of the Rebel Alliance, but not a full member. However, the rescued Sullustan technical staff worked together with General Crix Madine to devise a plan to end Operation Strike Fear by destroying the Invincible. The Rebels captured some engineers from Cygnus Corp and had them modify a shuttle to appear to be an Imperial vessel. Then, disguised as suppliers delivering cargo, Rebel agents got aboard the Invincible and planted a stolen Imperial warhead. The warhead exploded shortly after they left, destroying the Invincible.
After the Battle of Endor in 4 ABY, Tevv would finally join the Alliance, bringing with him a great amount of Sullustan rebels and becoming one of the signatories of the Declaration of a New Republic. The Sullustans became active members of the New Republic, and there was no more need for a Sullustan resistance movement.