The first year of the Dominion war consisted of two main phases; for the first six months the Allies were in a state of near constant retreat, loosing several major fleet actions to the Jem'Hadar. Throughout this period the initiative remained almost entirely with the Dominion.  All that changed with the operation to retake Deep Space Nine; the Federation and Klingon fleets inflicted a major defeat on the Dominion forces, smashing a 1,200 ship fleet and recapturing the station as well as convincing the wormhole aliens to deal with a further several thousand Dominion ships attempting to reinforce the Alpha Quadrant invasion forces. 
For the next six months the war entered something of a stand-off. Although fighting continued almost all along the front lines, including the Dominion's invasion of Betazed, neither side made a concerted effort to push into the others territory again. Many in Starfleet advocated a policy of "containment" - recommending that Starfleet should build its forces up sufficiently to deter further Dominion attacks without launching offensives of the own. However, Starfleet Intelligence's assessments of the Dominions shipbuilding and Jem'Hadar breeding programmes indicated that the balance of power would inevitably tip heavily in their favour once again over the next year. The only possible way to win the war was to launch an all out invasion of Dominion territory. Unfortunately, the Federation and Klingon Empires combined lacked the forces to ensure success.
The entry of the Romulans into the war towards the end of the year changed that equation. With the Dominion now fighting simultaneously along the Klingon, Federation and Romulan borders their forces were being spread more thinly. The addition of Romulan forces also gave the Allies the added firepower needed to mount a full scale invasion. The Chin'toka system was chosen to be the site of the first major attack, largely because intelligence had assessed it as having minimal defences.
Unfortunately for the Allies, the Cardassians had developed an extremely powerful orbital defence grid for the Chin'toka system. Hundreds of weapon platforms orbited the planet, each carrying heavy phaser banks, a thousand plasma torpedoes and regenerative shielding. Aware of the problem, the Allied fleet attempted to get to the system before the grid could be completed and activated. Initially they succeeded; several dozen of the platforms were destroyed in the opening attack. However, as the fleet closed on the planet the system was activated. A fierce battle raged for some time, with many Allied vessels destroyed or badly damaged while the defence grid suffered few losses. Fortunately for the allies, the crew of the USS Defiant determined that the entire grid was powered from a single location, an asteroid in orbit of the planet. The asteroid was also protected by regenerative shields, but the Defiant was able to use her navigational deflector to imprint a Federation warp signature on the asteroids systems; the defence grid turned on its own power system, destroying it completely. In the aftermath of the space battle the fleet began a surface assault on the planet itself. 
Although the Chin'toka battle was ultimately a success, it was a battle won more by luck than anything else. Had the Defiant not been able to disable the power system the fleet would certainly have had to retreat. On the other hand, the Cardassians new defence system has been demonstrated to have a critical flaw. Essentially, the huge effort put into developing and deploying this system has been wasted. Until the problem can be corrected, those planets which have been fitted with this model of defence grid will now have to be protected by Starships, which will further reduce the number of vessels available for offensive action. Fitting the weapon platforms with their own power systems will require a major re-design effort, one which cannot possibly be completed in less than six to twelve months. This may give the Allies a window of opportunity during which they can inflict heavy damage on the Dominion, perhaps even leading to a permanent shift of fortunes in the war.