Dominion

The Dominion was an interstellar empire whose base is in the Gamma Quadrant and whose seat of power is located on a rogue plent on the Omarion Nebula. It was founded and led by a group of Changelings called the Founders, who over some 2000 years conquered countless worlds across the Gamma Quadrant, maintaining order through their genetically modified servitor races, the Vorta and the Jem'Hadar.

First Contact
The Federation made an accidental first contact with the Dominion when Commander Benjamin L. Sisko, Commanding Officer of Deep Space Nine, his son Jake Sisko, Jake's best friend Nog and Nog's uncle Quark were briefly captured by the Jem'Hadar in the year 2370 on an uninhabited class-M planet in the Gamma Quadrant. Relations between the two interstellar powers were antagonistic from the very beginning when Jem'Hadar fighter ships destroyed the Galaxy class starship USS Odyssey, which had been sent to the Gamma Quadrant to rescue Sisko and his party.

Later that same year, the Dominion War began when the Dominion established an alliance with the Cardassian Union of the Alpha Quadrant and began sending ships through the wormwhole.