The Dominion War

The Dominion, a Gamma Quadrant empire ruled by the shape-shifting Founders and enforced by the Vorta and Jem'Hadar, gained a foothold in the Alpha Quadrant when Cardassia joined it in 2373. Open war broke out late that year, when Captain Benjamin Sisko mined the entrance to the Bajoran wormhole to stop reinforcements and the Dominion seized Deep Space 9.

The Federation and the Klingon Empire suffered heavy losses before retaking the station in 2374. The Romulans entered the war later that year, after Sisko helped expose a Dominion plot against them. The Breen then joined the enemy, attacking Earth and crippling the allied fleet with an energy-dampening weapon, while a Cardassian resistance led by Damar rose against the Dominion.

In 2375 the allies besieged Cardassia Prime. Odo cured the Founders of a deadly disease and persuaded their leader to surrender, ending the bloodiest conflict of the era. Cardassia lay in ruins, with hundreds of millions dead, and Sisko vanished into the Celestial Temple.