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.