The Dac Genocide was a campaign masterminded by Darth Krayt, the Sith Dark Lord and Empire's ruler, aiming to eliminate the entire Mon Calamari species. This was a retribution for their support of the Galactic Alliance Remnant during the Second Imperial Civil War.
Upon seizing the Imperial throne, Darth Krayt immediately tasked his subordinates with eradicating his adversaries throughout the galaxy. The Galactic Alliance Remnant, under the leadership of Admiral Gar Stazi, was a primary target. Darth Azard was the Sith assigned to oversee the Remnant's downfall. He delegated this task to Admiral Sha Dun of the Outer Rim Third Fleet, and later to Admiral Dru Valan after Dun's execution for failing.
Valan devised a scheme to ensnare Stazi, intending to lure him and his fleet to Dac. The bait was a new Star Destroyer under construction on the planet. However, the resulting battle turned into a debacle for the Empire. The Imperial fleet suffered significant losses, the new warship was commandeered, and the Remnant escaped with minimal casualties.
Following the Imperial fleet's defeat, Darth Krayt personally journeyed to Coral City, the capital of Dac, and summoned the Mon Calamari Council. He declared his dissatisfaction with the Mon Calamari's backing of Stazi and the Alliance, announcing that the entire species would face punishment. Ten percent would be immediately executed, while the remainder would be subjected to forced labor until their collective demise. Immediately, Emperor Krayt's loyal stormtroopers and Sith Lords began to attack every Mon Calamari on sight, and killed those Quarren that opposed them as well.
After Darth Krayt's departure, Darth Azard, a Quarren Sith, was put in charge of overseeing the genocide, assisted by Vul Isen, a Force-sensitive Givin scientist also serving the Sith. By the time the genocide was broadcast across the HoloNet, ten percent of Dac's Mon Calamari population had been murdered.
While thousands of Mon Calamari were consigned to extermination camps, where they were deprived of sustenance and medical care to ensure death by disease and starvation, others sought refuge in Dac's deep oceans. There, they were relentlessly pursued by the Imperial Army. However, the Mon Calamari Rangers emerged to challenge the Imperial onslaught, aided by Master Treis Sinde, a seasoned Imperial Knight. Simultaneously, the Sith unleashed their newest creation, a Sea Leviathan, to enforce Emperor Krayt's decree. Despite its immense destructive capability, capable of massacring an entire camp in a matter of minutes, the Leviathan was eliminated through the combined efforts of Master Sinde and the Rangers.
The Galactic Alliance's Rogue Squadron launched a mission to rescue a group of Mon Calamari refugees, utilizing cargo carriers for evacuation. When bounty hunters employed by the Sith attempted to trace the refugees back to Stazi, the Rogues successfully misled them by defending the wrong cargo carrier.
Shortly after Darth Krayt's demise, Lord Wyyrlok, the Voice of the One Sith and the Empire's new leader, commanded Vul Isen to initiate the Final Protocol. This involved poisoning Dac's waters to eradicate all life on the planet, freeing up Imperial forces for deployment elsewhere. Lord Wyyrlok disregarded Lord Azard's reminder of the Quarren collaboration and the neutrality of individuals of other species, decreeing that they would be allowed to evacuate the planet but would receive no assistance. Isen released viral spores, which, carried by oceanic currents, would eliminate all life within a week.
Three days following Wyyrlok's edict, Rogue Squadron conducted a reconnaissance mission on the planet, discovering a section of the ocean covered by a mass of millions of deceased Mon Calamari and Whaladons. They promptly set out to inform Admiral Gar Stazi, although Andurgo broke formation and engaged incoming Predator fighters.
Upon learning this, Stazi decided to save the Mon Calamari. His fleet returned to Dac and, after repelling waves of Sith-Imperials, managed to rescue a portion of the planet's population. Although numbering in the millions, this represented only a small fraction of the planet's 27 billion inhabitants.
Krayt had two goals for the genocide: to punish the Mon Calamari and to deter future resistance to his empire.
While it did force some systems into submission, it outraged many other planets and systems. These systems "allowed" ships from their planetary fleets to join the Galactic Alliance Remnant, while many Mon Calamari that were off world at the time joined the Remnant. These actions significantly augmented Stazi's forces.
The poisoning of Dac, which resulted in billions of deaths, also spurred more individuals to oppose the Sith Empire. It also destroyed diplomatic relations with the empire's neighbors, the Chiss Ascendancy and the Hapes Consortium (who refused to even speak with Sith-Imperial representatives after the poisoning was announced). The subsequent devastation of Da Soocha and Napdu also led the Hutts to join the efforts against the Empire.