Cardassians: Cruel, arrogant, violent.
Cardassians and the Cardassian Union were introduced in The Wounded. They were once a peaceful, spiritual people who collected works of art from all over the Alpha Quadrant, but their planet--Cardassia--lacked natural resources. The entire planet was stricken by famine and disease until the military took control of the government and expanded Cardassian borders, building fleets of warships and invading nearby worlds. Bajor--for one--was occupied for fifty years. Sometime before 2347 the Cardassians attempted to expand into Federation space and war broke out, lasting around twenty years.
Shortly after the Cardassians withdrew from Bajor, a Federation presence was established in Terok Nor--renamed Deep Space 9--to assist the Bajoran Provincial Government in rebuilding Bajor only to discover a wormhole to the Gamma Quadrant. (Emissary), Roughly four months later, the Federation-Cardassian borders were redefined, with the two sides buffered by the Demilitarized Zone. However, the Cardassians harassed the Federation colonists in the DMZ who then retaliated by forming a resistance movement known as The Maquis.
Around the same time, the Obsidian Order--the Cardassian intelligence agency--began to gain power, becoming almost the Section 31 of Cardassia. However, it was destroyed when it allied with the Tal Shiar--the Romulan version--in a preemptive strike against the Dominion--a new threat from the Gamma Quadrant. (The Die Is Cast)
In January of 2372 (Stardate 49011), the Klingon Empire attacked the Cardassians believing the Detapa Council had been infiltrated by the Dominion. (The Way of the Warrior, Part I and Part II) The attack was lead by General Martok who, it turned out, had been himself replaced by a shapeshifter--the leaders of the Dominion. (In Purgatory`s Shadow)
Then, sometime between October 2373 and February 2374, with a Dominion attack on Deep Space 9 imminent, Gul Dukat announced the Cardassian Union's joining with the Dominion, shocking not only the Federation but most Cardassians as well. At the same time, Gul Dukat announced his ascension as leader of the Cardassian Union. Five days later, the Maquis were all slaughtered by the Dominion. (All but those on Voyager, that is.)
The Cardassians (and therefore the Dominion) captured Deep Space 9, (Call to Arms) but the Federation managed to plant the wormhole with self-replicating mines preventing the Dominion from sending in reinforcements.
Unfortunately for the Federation, Gul Damar discovered a way to disable the self-replication of the mines and completed the procedure and fired on the minefield seconds before O'Brien and Nog disabled the weapons in hopes to prevent just that. The USS Defiant attacked Deep Space 9 and managed to take it back when the Prophets destroyed the entire Dominion fleet on its way through the wormhole. Gul Dukat was captured after his daughter was killed by Gul Damar who was then promoted to Legate. (Sacrifice of Angels)
Under the leadership of Damar, the Cardassian Union, along with the Dominion, continued to gain ground over the Klingon-Federation alliance, and even after Sisko and Garak tricked the Romulans into breaking their nonaggression treaty with the Dominion and joining the alliance (In the Pale Moonlight) they still managed to keep the upper hand.
Damar, however, was not happy. While he had hoped that Cardassia joining the Dominion would strengthen their power, he felt that they were no longer in control of even their own planet, having to report to Weyoun and the Founders, and with Cardassian troops sacrificed seemingly meaninglessly and without his permission. Shortly after the Breen joined the Dominion--almost guaranteeing the Dominion's victory--Damar organised a revolt. A Cardassian named Broca became Legate.
The revolt started out just as a small legion of troops headed by Damar, but during the final assault on the Dominion by the Federation-Klingon-Romulan alliance, Damar managed to get an open revolt started on Cardassia itself with the civilians joining in and the Cardassian fleet turned during battle and assisted the alliance. The Female Shapeshifter ordered every Cardassian on the planet killed.
With the Cardassian fleet helping the alliance and the rebel's attack on the Dominion headquarters on Cardassia the Dominion surrendered, ending the Dominion War, but leaving Cardassia in shambles.
In the Mirror Universe, the Cardassians formed an alliance with the Klingon Empire after destroying the Federation.
The Star Trek Encyclopedia
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