The Archanis sector was a region of space near the Federation-Klingon border. The sector was originally claimed by the Klingon Empire, but was relinquished to the United Federation of Planets a hundred years before 2372. It contained the planet Archanis IV, as well as a number of Federation starbases and military installations. (DS9: "Broken Link")
In late 2372, Chancellor Gowron demanded that the Federation relinquish the sector to the Klingons, at the urging of whom he believed to be General Martok. (DS9: "Broken Link") In reality, this Martok was a Changeling who had replaced the real Martok over a year earlier. A Klingon task force took the sector shortly after, starting the Federation-Klingon War. (DS9: "Apocalypse Rising")
In 2373, Starfleet attempted to retake the Archanis sector. The effort was led by the USS Tecumseh and the USS Rutledge. (DS9: "Nor the Battle to the Strong")