The Battle of Cardassia was the final battle of the Dominion War, fought in late 2375. The allied forces of the United Federation of Planets, the Klingon Empire, and the Romulan Star Empire launched an invasion of the Dominion-held Cardassian Union, with the goal of capturing the Dominion's capital on Cardassia Prime. The battle would ultimately lead to the Dominion's unconditional surrender of all forces in the Alpha Quadrant.
The events of the battle must also be considered alongside concurrent events on Cardassia Prime in the final stages of the Cardassian Rebellion, led by Legate Damar. The sabotage committed by the Cardassian insurgents played an important role in disrupting Dominion communications and support behind the front lines, and ultimately led to the Cardassian ships in the battle switching sides. Before the battle was over, however, more than 800 million Cardassian civilians would be killed by Dominion genocide, leaving the once-proud capital planet in ruins. (DS9: "What You Leave Behind")
By late 2375, the Dominion's massive offensives into the Alpha Quadrant had stalled, leaving its forces embroiled in a war of attrition spread across multiple sectors that it could not win under the present circumstances. Reinforcements through the Bajoran wormhole had been blocked since the beginning of the war (c.f. Battle of Deep Space Nine), and the existing industrial infrastructure in Cardassian territory was insufficient to maintain the offensive for a prolonged period of time.
The Dominion's last hope for a quick victory was its alliance with the Breen Confederacy and their mysterious energy dampening weapon, against which the allies had no defense. Although the Breen's weapon had a major effect in its first uses, particularly at the second Battle of Chin'toka, the Dominion's chance at a quick offensive was lost by Legate Damar's rebellion, which caused massive disruptions behind the lines and forced the Dominion to devote considerable resources to quelling the uprising. By the time Damar's resistance cells were eradicated, the Federation and the Romulans had developed countermeasures after acquiring a stolen example of the weapon. (DS9: "Tacking Into the Wind")
Apparently becoming disillusioned with the war, the Female Changeling ordered Dominion forces to effect a complete withdrawal from all territories held inside the Federation and the Klingon and Romulan empires. It was hoped that by reverting to pre-war territories, the Dominion could convince the Federation and her allies to sue for peace, rather than commit to a bloody invasion that would cost millions of lives. With less territory to defend, the Dominion could repel any attack and build up its forces for a renewed invasion several years later.
This move could have signaled an end to the war — the withdrawal of all enemy forces from conquered territories was one of the major aims of the war for all allies. However, the Founder seriously miscalculated the allies' resolve to win the war at any cost. In addition, Captain Benjamin Sisko and Admiral William Ross recognized the threat of allowing the Dominion to remain in Cardassian space unchallenged. Therefore, the allies agreed to launch an invasion of Cardassia Prime itself, with the aim of decapitating the Dominion leadership and throwing its hierarchy into chaos. (DS9: "The Dogs of War")
Phase One: Invasion
Launching their attack fleet from Deep Space 9, the allied fleet, more than 1,000 ships strong, made a beeline directly for Cardassia, crossing the five light-year distance in approximately one and a half days. The Female Changeling ordered as many ships as possible to meet them, perceiving the nearing endgame of the war.
As the two enemy fleets made their final approach, the Female Changeling, the Vorta Weyoun, and Breen Thot Pran were inside Dominion Headquarters making final plans for the attack. Suddenly, nearly every Dominion installation on the surface of Cardassia lost power — the Cardassian rebellion, led by Legate Damar, had inspired the Cardassian populace to rise up and overthrow their Dominion occupiers. The Dominion was completely cut off from any support from the surface of Cardassia.
In space, the two fleets bore into each other with abandon, the battle degenerating into a melee of close-quarters combat between the highly maneuverable Starfleet and Breen ships and the less-maneuverable but heavier Dominion, Cardassian, Klingon, and Romulan ships. Although the Dominion's lines were spread relatively thinly in the center of their formation, the Jem'Hadar forces heavily hammered the Romulan lines, destroying the Romulan flagship IRW D'ridthau. Captain Sisko marshaled several attack wings to reinforce the Romulan lines, while Admiral Ross and Chancellor Martok's forces targeted the Dominion center.
On Cardassia, when the Dominion regained access to their communications, they launched hard and swift punishment for the Cardassians' betrayal of the alliance. The Female Changeling ordered Jem'Hadar forces in orbit to bombard Lakarian City, destroying it utterly and killing two million men, women, and children in a matter of seconds. Weyoun announced to the public that another Cardassian city would be destroyed for each further act of sabotage.
In space, the allied lines were in danger of crumbling under pressure from the Dominion's right and left flanks. Losing ships at an accelerating rate through the protracted battle, success was in jeopardy as the Dominion pressed their advantage.Starfleet and the Romulans were preparing to retreat when the impossible happened — the Cardassian fleet switched sides, turning on their erstwhile Dominion allies in response to the destruction of Lakarian City. Taking advantage of the sudden chaos amid the enemy forces, the allies rallied an attack on the Dominion's center, punching into the core of the defending fleet.
Furious, the Female Changeling ordered the Dominion and Breen forces to disengage and retreat to Cardassia Prime, proclaiming "there will be no more running." The defending forces withdrew from the battle, leaving the allies victorious.
Phase Two: Final Solution
The battle was not yet over, however. Captain Sisko convinced Chancellor Martok and Admiral Ross to press their advantage, despite having already lost an astounding 30% of their forces during the battle. Even with the Dominion's influence restricted to Cardassia Prime itself, its potential for rebuilding its forces would only prolong the inevitable. Recognizing this, the allies chose to press onwards.
On Cardassia, the Female Changeling, suffering from the final stages of the debilitating Founders' disease, seemed to grow completely frustrated with the Dominion's allies, ordered the Jem'Hadar to begin exterminating the entire Cardassian population. Rampaging across the planet, the Jem'Hadar summarily executed every civilian they came across and began destroying residences building by building.
Damar, along with Kira Nerys, Elim Garak, and a handful of Cardassian volunteers, mounted a daring assault against the Dominion headquarters compound, seeking to capture the Founder alive and force an end to hostilities. With so many of the Jem'Hadar guards sent to destroy the Cardassians, there were only a few left to guard the shapeshifter. Although Damar was tragically killed during the short but sharp fight, most of the remaining rebels fought their way to the headquarters' briefing room, capturing both the Female Changeling and Weyoun.
In orbit, the allies found a daunting sight, with thousands of Jem'Hadar and Breen warships, plus thousands of the Cardassian orbital weapon platforms last encountered at the first Battle of Chin'toka a year before. Unwilling to turn back, they prepared to launch a three-prong attack on the Dominion's defenses — an attack that was projected to cost up to 40% of their remaining forces, without even accounting for the following ground assault.
As the rebels on the surface tried to convince the Founder to surrender, her chilling plan became clear — by ordering the Jem'Hadar and the Breen to fight to the very last man, she sought to make the allies' victory so costly that it would be only pyrrhic. With such a great cost of victory, she hoped to ensure that the Alpha Quadrant powers would never again threaten the Dominion.
Before the final assault began, however, Odo, recently cured of the Founders' disease, volunteered to try to convince the Female Changeling to surrender to the allies. By Linking with her, Odo managed to cure her of the disease and persuade her to call for an end to the fighting. The battle — and the war — were suddenly over.
The instrument of surrender was signed at Deep Space 9 only days later. In it, the Dominion agreed to withdraw all of its forces to the Gamma Quadrant, and the Cardassian Union was occupied by the allies.
The result of the battle can be considered fortuitous, at the least. Had the Founder not chosen to surrender, the Jem'Hadar would have fought to the last man on Cardassia and on every other world in the Alpha Quadrant — requiring a mop-up operation that would probably have taken years, and required incredible resources that the allies may not have had the stamina to provide.
As it was, the battle was nothing short of devastating for Cardassia, decimating a huge portion of its surface and killing over 800 million civilians. Hundreds of allied warships were lost at the cost of tens of thousands of lives. It was only in avoiding the final assault on Cardassia itself that more bloodshed was avoided.