The Alliance to Restore the Republic, also known informally as the Rebel Alliance was a loose alliance of planetary, system, and sector-level insurrectionist factions. Members of the Alliance were known as "Rebels" or the derogatory "Rebel scum" used by Imperials and loyalists. They were generally united in common cause, against a common enemy in the form of the First Galactic Empire. In order to achieve their primary goal in restoring the former Third Galactic Republic, the Alliance aimed to remove Emperor Thoron from power, and end his hegemonic New Order from the galaxy.

The origins of the overall anti-Imperial movement dated back to 119 BrS, shortly before the Republic's transformation into the Empire. Some of the Alliance's core founders, such as senators Andreus Prestor and Cheron Béne of the Loyalist Committee, joined the Restorative Delegation in its opposition against the authoritarian leadership of then-President Mudell Thoron. In 113 BrS, barely a year into the Empire's existence, military resistance had already been formed in opposition to the new regime; one of which was a group of insurgents known as The Six, created by the fugitive  Firus Orel. In 2M19 CE, several resistance groups were unified into a single rebellion, thus creating the Alliance.

The Galactic Civil War erupted into a furious two front war with the fledgling Alliance challenging the Empire for control of the East Galaxy. Though vastly outnumbered in manpower, starships, weapons and various other resources, the Rebels themselves possessed a strong will to fight. By and large, the Alliance was composed of well-trained soldiers and brilliant commanders, some of whom dedicated their lives to the Rebellion after defecting from the Empire due to the atrocities that were committed by the Imperial regime. After securing early victories against the Empire on Kronus and Toprawa, the Rebels achieved one of their most significant triumphs at the Fourth Battle of Vargoth, in which an Imperial Superstation—codenamed DS-3—was destroyed. In 2M23, roughly four years after the destruction of the Superstation, Supreme Commander Merric perished during the Battle of Corellia. In the wake of the victory at Corellia, the Rebel Alliance reorganized itself into a more formal state that was originally known as the Alliance of Free Systems before its reorganization into the Fourth Galactic Republic.