Literally the only demand made by the dominion was they stop going through the wormhole and making incursions into.their sovereign space. The federation has a neutral zone with the romulans that has lasted like 100 years or more by that point, but if there's a wormhole it's somehow their god given right to poke around someone else's territory? Not even to mention the Cardassian/Romulan pre emptive attack on the Founders homeworld. Prior to that they just sent spies and harrased ships in the gamma quadrant. Seems like a more than reasonable cause for war to me.
Omg, and the end result is a more militarized federation, billions dead on both sides, the dominion being in basically the same position it would have been had they just listened in the first place and stayed on their side of the wormhole which was part of the treaty ending the dang war. The only benefactor long term was the Federation who's uneasy allies and enemies had exhausted their forces either fighting or being occupied during the war is clearly coming out a galactic hegemony after. The Dominion War was the war on terror.
War, what is it good for?