Earlier in the Dominion War, the Federation had deliberately gambled the station in order to buy time for a strike on Dominion shipyards. At the time, it was believed that the improvised minefield guarding the wormhole would be sufficient to stop the Dominion from bringing in reinforcements from the Gamma Quadrant; however, intelligence from a resistance cell on the station revealed that the Cardassians had devised a way to disable the mines.
With insufficient time to gather the required forces, a 600-strong Federation fleet departed for DS9, hoping to rendez-vous with Klingon reinforcements along the way. In response, the Dominion deployed a 1254-strong fleet of Jem'Hadar and Cardassian vessels, leading to a stand-off several light years from the station. Taking advantage of a Cardassian feint intended to draw Federation vessels into the Dominion line, the Defiant pushed through the Dominion fleet, quickly losing it's escorting vessels due to enemy fire. The unexpected arrival of a small Klingon fleet allowed the Defiant to break through the line and head to DS9, where the ship entered the wormhole in a desperate bid to stop the Dominion reinforcements from reaching the Alpha Quadrant.
Due to an intervention by the so-called wormhole aliens, the Dominion reinforcements were wiped from the wormhole. Their loss, combined with the imminent victory of the Federation/Klingon fleet, prompted the Dominion to abandon DS9.
While the recapture of DS9 did not end the war - and indeed, the following months would prove to be militarily disastrous for the Federation - it did provide an invaluable psychological advantage to the demoralised Federation, as well as cutting off the Dominion forces in the Alpha Quadrant from further reinforcements.