Archanis sector

From Memory Alpha, the free Star Trek reference

The Archanis sector is a region of space between the United Federation of Planets and the Klingon Empire, named for the Archanis system. The main planet is Archanis IV. The sector was originally Klingon territory, but was relinquished to the Federation in the mid-23rd century. It contains a number of Federation starbases and outposts. (DS9: "Broken Link")

As Kira Nerys stated that the Klingons had given up their claim "one hundred years" prior to the events of 2372, it is possible that this was a result of the 2267 "Treaty of Organia".

In late 2372, Chancellor Gowron demanded that the Federation abandon the sector to the Klingons, at the urging of General Martok, who had been replaced by a changeling. Shortly after, a Klingon task force took the sector starting the Second 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")