The Dominion fired the first shot.
When the GQ terminus of the wormhole was first discovered it wasn't yet Dominion in territory. So Starfleet sends ships and more or less claims it.
The Dominion destroys ships, colonies. It doesn't send diplomats to say, "Would you mind respecting our territory."
You can call it provocative, but Starfleet legally mined an area of space it controlled. What did those mines do, close the door to ships from either side. In essence Starfleet was not going to venture into the GQ and Dominion space anymore. Exactly what the Dominion wanted.
You also have to bear in mind the Founders didn't trust solids, so it was likely no matter what they did sooner or later they would have attacked. It was only because of Odo's experiances with solids that he was able to convince the female founder that she could trust solids esp. the Federation to keep the other powers inline.