Initially named the Imperious, the Alliance represented a substantial and formidable war vessel created by the Galactic Empire under the rule of Darth Krayt. It served as the original prototype for the Imperious-class Star Destroyer, a Star Destroyer design that surpassed the Pellaeon-class in both size and power. It functioned as the personal flagship for Galactic Alliance Admiral Gar Stazi.
Darth Krayt, the Dark Lord of the Sith and Emperor presiding over the new galactic empire, issued a directive for the development of a novel warship class capable of overwhelming any vessel type utilized by the Empire's numerous adversaries. In response to this directive, Moff Rulf Yage, who headed the Imperial Navy, put forward the concept of the Imperious-class Star Destroyer, envisioned as an enhanced version of the Pellaeon-class.
The construction of the Imperious took place within the Mon Calamari Shipyards during 137 ABY, an era when these shipyards were under the control of a breakaway faction within the Empire. It stood out as one of the largest vessels within the Empire's fleet, and was regarded as the crown jewel of the Imperial Navy. The Imperious's inaugural voyage was intended to be carried out with minimal crew staffing.
At that time, the Galactic Alliance Remnant stood as a principal challenger to Krayt's dominion. Upon learning of the Imperious, Admiral Gar Stazi, who commanded the Alliance, determined that acquiring the warship was a necessity. Stazi formulated a strategy to seize the Imperious, enlisting the assistance of his longtime comrade, Gial Gahan.
However, on the day Stazi and his fleet launched their operation, they found themselves ensnared. Admiral Dru Valan, an Imperial officer with a personal grudge against Stazi, had become aware of Stazi's intentions and orchestrated a scheme to either capture or eliminate Stazi and annihilate his fleet. Unbeknownst to Valan, Stazi had anticipated the trap and turned the Imperials' plan against them.
Stazi commanded his fleet to attack the Outer Rim Third Fleet. When Valan gave the order to return fire, including from the shipyards, the shipyards instead joined the Alliance in targeting the Imperial fleet. This was due to the shipyards having been compromised by Rogue member Monia Gahan. Simultaneously, the Alliance reclaimed control of the Imperious, as the stormtroopers who had seized it were, in reality, Alliance commandos in disguise. Under the leadership of Hondo Karr, they steered the ship away from the shipyards, successfully extracting it from the system. Subsequently, the Alliance fleet retreated behind the planet Dac, managing to escape and reach their designated rendezvous point. The Imperious was now under the control of the Galactic Alliance Remnant, who proceeded to activate its weapon systems.
Stazi designated the ship as his new flagship, succeeding the Indomitable.
However, the Alliance was unaware that Roan Fel's Empire-in-exile had sabotaged the Imperious. Activating the ship's weapons would trigger the detonation of three sets of explosives, resulting in the vessel's destruction. Fortunately, Monia Gahan and Imperial Knight Sigel Dare managed to alert Admiral Stazi. The bombs were disarmed, and Stazi, impressed by Fel's willingness to assist him, requested Dare to inform Fel of his openness to resuming negotiations for an alliance against the Sith. He also renamed the ship the Alliance.
Meanwhile, Darth Krayt was enraged by Stazi's escape with his most advanced warship, and he ordered the genocide of the Mon Calamari for two reasons: to punish the Mon Calamari and to deter any further resistance against his empire. Although this action did intimidate some systems into compliance, it also provoked outrage in many others, leading them to contribute ships from their defense fleets to bolster Stazi's forces. This effect was likely amplified by Krayt's death on Had Abbadon.
As the vessel underwent proper outfitting for combat, the symbol of the Galactic Alliance was emblazoned on its sides, reminiscent of the Lusankya when it served the New Republic over a century prior.
Under the command of Admiral Stazi, the Alliance engaged the Coruscant Third Fleet during the Battle of Ralltiir. Unbeknownst to Stazi and his crew, a traitor was present on board. The traitor's actions led to an assassination attempt on Stazi and an attack by the First Coruscant Task Force. Fortunately, the assassination attempt failed, and the Imperial fleet was outmaneuvered and forced to retreat. The traitor, despite feeling deep remorse for his actions, was imprisoned and faced the prospect of a court-martial and execution.
The Alliance was stationed above Dac when the Sith introduced toxins into the waters of the ocean planet, aiming to eradicate all life. However, Admiral Gar Stazi was determined to attempt an evacuation of the native Mon Calamari.
The Alliance spearheaded an assault on the Sith forces positioned in orbit around Dac, successfully compelling them to withdraw. When the Outer Rim Third Fleet responded, the Alliance once again led the Remnant's counterattack. Although the initial engagement was relatively balanced, the arrival of Imperial forces loyal to Roan Fel shifted the advantage to the Alliance. The Sith retreated once more, and the evacuation efforts proceeded. Nevertheless, only approximately twenty percent of the planet's 27 billion inhabitants were rescued before the toxicity became insurmountable.