In the fictional `` Star Trek '' universe , the Dominion War is a conflict Hostile_encounter between the forces of the Dominion , Cardassian Union and , later , the Breen Confederacy against the Alpha Quadrant alliance of the United Federation of Planets , the Klingon Empire and , later , the Romulan Star Empire .

The Dominion War arcs present Presence themes that challenge the values of the characters in a manner not attempted in earlier series of `` Star Trek '' , and have received Receiving a mixed Cause_to_amalgamate critical response Response .