Klingon-Cardassian Alliance
The Klingon-Cardassian Alliance was the dominant power of the Alpha Quadrant in the mirror universe throughout most of the 24th century.

History 
The Alliance was the historic union of two former enemies, the Klingons and the Cardassians, in the face of aggression from the Terran Empire. The Alliance itself was led by a Regent, who delegated authority to various Intendants who administrated the individual sectors of Alliance territory. As of 2372, the Alliance was ruled by Regent .
The Alliance conquered the Terran Empire, following a series of reforms by , the leader of the Empire, that had left it vulnerable to attack. When the Alliance was finished, the s and the Vulcans were reduced to a slave race filling the mines of various Alliance planets.

The Bajorans became a major partner in the Alliance in the later 24th century, after their liberation from the control of the Terran Empire. However, the Bajoran rule would end up leading to one of the greatest threats to Alliance control.

On station , a bizarre accident in the Bajoran wormhole brought a Federation runabout from the primary universe into the mirror universe. The runabout's crew, Kira Nerys and Julian Bashir, were only aboard the station for a few days, but their presence incited a rebellion among the Terrans, led by . ()

The Alliance tried (futilely) to crack down on the Terran Rebellion, but the rebels managed to elude the Alliance at almost every turn. Although Sisko was killed by the Alliance in 2371, the rebels continued to fight on. By taking refuge in the Badlands, the rebels were able to avoid a confrontation with the Alliance fleet almost constantly. ()

In 2372, the Alliance suffered a humiliating defeat when the rebellion managed to capture Terok Nor. Regent  personally led the assault fleet that attempted to recapture the station, but that fleet was defeated thanks to a powerful new warship the rebels had hurriedly constructed. ()

As if the Terran Resistance Forces' initial victories were not humiliating enough, the Alliance suffered a further defeat in 2375 during an operation in which Worf attempted to obtain a cloaking device from the prime universe. Regent Worf himself was captured along with the Alliance's flagship by the rebels and taken to Terok Nor in chains. The final fate of the Alliance after Regent Worf's capture is unknown. () 

While the Bajorans of the mirror universe have been influential members of the Alliance ever since the defeat of the Terran Empire,  has apparently been attempting to lead Bajor in rebellion against the Alliance. Her reasons for this are unclear, although it is most likely a simple power grab on her part. ()

Subject species 
Klingon
Cardassian
Bajoran
Human ()
Vulcan
Trill
Ferengi

Ships used by the Alliance 

Klingon Bird-of-Prey
Negh'Var warship
Regent's flagship

Appendices

Appearances 
DS9
 (Season 2)
 (Season 3)
 (Season 4)
 (Season 6)
 (Season 7)

Apocrypha
There are several divergent stories as to how the Alliance was formed:
In Dark Victory, the second novel of William Shatner's Mirror Universe Trilogy,  explains to his counterpart, James T. Kirk, that he united the Klingons and Cardassians as an effort to regain power after being dethroned by his prime minister, . However, the Alliance turned on him as well, and he went into cryogenic stasis with his loyal generals for what was intended to be a one-year journey - which instead became 78 (mirroring Kirk's 78-year displacement in the Nexus).

The Mirror Universe series, which began in 2007, tells the story of both the Alliance's initial founding and the downfall of its occupation of the former Terran Empire. In The Sorrows of Empire, the formation of the Alliance is actually part of a master plan by  to destroy the Terran Empire and replace it with a government similar to that of the United Federation of Planets, which he discovered through his mind-meld with Dr. McCoy in ; he believes the union of these particular nations will bring out "the worst qualities of both", citing incompatible world-views that will eventually bring both nations to ruin. Spock states clearly, at the mirror universe's Khitomer Conference in 2293, that the downfall of his empire will bring about the downfall of the Terran Empire's enemies. As predicted, the Alliance conquers the nascent Terran Republic in 2295, killing Spock and his wife , and begins occupying many of its worlds. Spock's supporters, particularly his operatives on Vulcan, become "willing slaves" of the Alliance in order to lay the groundwork for the Terran Rebellion against the Alliance. In Rise Like Lions, the races that make up the Rebellion eventually win their freedom and fulfill Spock's vision of a democratic republic with the foundation of the Galactic Commonwealth in 2378.

In Star Trek Online, a reestablished Terran Empire invades the prime universe through an anomaly in the Arawath System. During a mission to take an Orb to the mirror universe and switch it with its counterpart, thereby closing the portal, the player character briefly allies with the Klingon-Cardassian Alliance to defeat Terran Empire forces guarding the mirror version of the Orb.

External links 
 
 

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Mirror universe
Governments