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.
I also forgot something else, during this time in trek there were some let's say very interesting interpretations of the prime directive. So if the federation and Starfleet knew about the cardassian's brutal occupation of Bajor before Wolf-359 even happened, I wouldn't be surprised one bit if they publicly took issue with it and privately didn't do much because it would be "messing with an internal matter of another nation". Which is one of the things the PD prohibits doing.
Edit: Good god do I want to go on a rant at how useless the prime directive is on a morality level.