system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek: DS9] In the season 5 finale, Starfleet is unable to send reinforcements since the ships are needed elsewhere. Where is this?
gpt
Starfleet was engaged in a massive joint operation with the Klingons to eliminate a major Dominion shipyard. 

Taking advantage of the Dominion's focus on the assault on DS9, the Klingons and the Federation launched a major attack against the Dominion shipyards on Torros III. By concentrating its forces on a single operation, the Federation-Klingon units attained local superiority of force against Dominion's absolute numerical superiority in theater. Allied units breached Dominion lines and established a salient towards the Torros system, while a special taskforce entered the system proper and suppressed system defences long enough to affect the complete destruction of Torros III's shipbuilding infrastructure. Once the shipyard was eliminated, Federation and Klingon units withdrew behind their own lines and closed the salient. 

The Dominion had heavily invested in the Torros III shipyard. Its output and location would have given the Dominion a significant advantage against attrition for several sectors. The destruction of Torros III forced the Dominion to rely on shipyards in systems located deeper within Cardassian space, slowing the tempo of Dominion operations.