Synopsis
In "Emissary", the pilot episode, the United Federation of Planets dispatches Commander Benjamin Sisko to take command of the space station Deep Space Nine. The station is located near a stable wormhole located in the Alpha Quadrant, which leads to the Gamma Quadrant of the Milky Way Galaxy, nearly 70,000 light years away. Deep Space Nine is moved from the orbit of the planet Bajor to the Alpha Quadrant terminus of the wormhole to lay claim. Starships begin to enter the wormhole to explore, colonize and trade. The crews on the ships were unaware that they are entering a region of space controlled by the Dominion, a union of planets ordered by force and intimidation.
Deep Space Nine's Ferengi bartender, Quark, makes contact with the Vorta, a Dominion member race. However, he and Sisko are captured by the Jem'Hadar, the soldiers of the Dominion. The Alpha Quadrant group is rescued, but the Federation ship USS Odyssey is lost in the attempt to return home, and colonies are destroyed as a warning not to re-enter Dominion space. Later, it is revealed that a race of shapeshifters, known as "Founders", are the rulers of the Dominion, and that Constable Odo is of this species. Members of the Cardassian Obsidian Order and the Romulan Tal Shiar intelligence factions plan to eradicate the Founders and their homeworld, but are themselves deceived by a shapeshifter and ambushed.
The Founders initiate a campaign of sabotage and terror against the Alpha Quadrant, which leaves many governments fearful of infiltrators, who are able to assume any physical form. When Earth is attacked, a band of Starfleet officers illegally attempt to impose martial law at the heart of the Federation. The Klingon Empire invades Cardassia in the inaccurate assumption that the Dominion is influencing its government. Later, the Federation suspects the Klingon Chancellor, Gowron, of being a shapeshifter. This turned out to be a ploy by the Dominion so that the Federation would assassinate Gowron and further intensify the rift between the Federation and Klingons due to the Klingon invasion of Cardassia. During the assassination attempt, the Federation realized that Klingon General Martok was the actual shapeshifter. It would turn out that Martok, Dr. Julian Bashir and others have been held captive at a prison camp in the Gamma Quadrant while shapeshifters took their place in the Alpha Quadrant. Shortly before their escape, the Dominion succeeds in urging the Cardassians to enter an alliance during the confusion, establishing its presence in the Alpha Quadrant. Realizing the danger, the Federation and Klingons join forces to slow the Dominion build-up, co-operating to plant a minefield across the entrance to the Bajoran Wormhole as a rescued Martok is assigned as a permanent Klingon commander at Deep Space Nine.
Nevertheless, the Dominion begins to advance, and seizes control of Deep Space Nine. After a brief retreat, Sisko executes a successful return to the space station, but the wider conflict continues. More setbacks hinder the Alpha Quadrant alliance as additional races, such as the Breen, offer their support to the Dominion. Questionable tactics are adopted in the search for victory, including the dissemination of an engineered virus among the Founders by a shadow Federation group called Section 31. A ruse involving a murder is used to enlist the help of the Romulans against the Dominion, and dissatisfactions lead the Cardassian leader, Legate Damar, to launch a successful resistance movement against his former Dominion comrades. Eventually, the Dominion is forced back to the planet Cardassia Prime where it is cut off from reinforcements. The female shapeshifter in command informs Odo that they would fight to the end in order to prevent any counter-attack by the alliance into the Gamma Quadrant. Odo assures her that the Federation would not do that while the other parties would be too weak to. After linking together, Odo cures the female shapeshifter of the biological disease afflicting her and the other Founders with the antidote he received and the Dominion agrees to surrender.
Read more about this topic: Dominion War