The Abridon Nationalists were a resistance group fighting to liberate their homeworld of Abridon from the Galactic Empire. In 3 ABY, they were able to seize the planet in cooperation with Rebel Alliance forces. The Abridon Government Council opened negotiations to join the Rebel Alliance, which was represented by five dignitaries, including Jedi hero Luke Skywalker.
However, their control was short-lived. Within three days Grand General Malcor Brashin and General Brenn Tantor arrived on the Imperial Star Destroyer Inquisitor. Tantor landed on the outskirts of Abridon's capital and swiftly evicted the Nationalists and their Rebel allies, recapturing the Government Center and the capital's Imperial base. In the attack, he captured a Nationalist leader, Hamman Flatt. Flatt, the planet's lieutenant governor, offered information to Tantor in hope of mercy, giving up the dignitaries. Flatt was put in a prison camp and Tantor was able to capture the dignitaries, including Skywalker, and completely wipe out the Rebel presence.
Even with the Alliance gone, the Nationalists remained. The industrial city of Sayan became their stronghold. Nationalists engaged in months of battles with Imperial forces until the Empire had had enough. The Empire placed artillery platforms next to the shipyards and began systematically leveling the city.
Into this situation stepped Brenn Tantor yet again. Now having defected to the Alliance, he captured the Government Center yet again, freed Flatt, captured the Sayan shipyards, and completely exterminated the Empire's presence in Sayan. The Abridon Nationalists gladly joined the Alliance, just in time to provide A-wing fighters for the imminent Battle of Endor.