Dominion War

The Dominion War is an extended plot of Star Trek: Deep Space Nine: a conflict between the Dominion, the Cardassian Union and eventually the Breen Confederacy on one side and the Alpha Quadrant alliance of the United Federation of Planets, the Klingon Empire and later the Romulan Star Empire on the other. The Dominion, a powerful Gamma Quadrant empire ruled by the shapeshifting Founders, was introduced in the second season; open war began at the end of the fifth season, when the Dominion briefly occupied Deep Space Nine, and lasted until its defeat in the series finale. Developing the war shifted the series from an episodic to a serialised format.