Beta Quadrant.
The Kinshaya are the dominant species of an interstellar polity somewhere in the Beta Quadrant. While they have little contact with the Federation, they are known to border the Klingon Empire and have had numerous conflicts with the Klingons dating back at least to the early 23rd century. (TOS novel: The Final Reflection)
The Klingons first discovered them near the T'Dakka star system and found a race that perhaps surpassed them in their war-like nature which is described as near berserker-like qualities. The name means 'demon possessed' within the Klingon language. Eventually, this sparked the 'Demon War' between the two groups which forced the Klingon Empire to divert forces from the Federation and Romulan border to the location that is known as 'Demon's Rift' where the threat that the Kinshaya posed was located at. Eventually, the war ended but resulted in no victory for either side and only resulted in the development of a 'cold war' between the two with hositlities still remaining between the two nations. (FASA RPG: The Klingons)
It is unknown if the Federation possesses any knowledge of this race but considering the location of their territory on the far side of Klingon space, such an act would be unlikely. At least, not when the Klingons were at war with the Federation. ([citation needed] suspected FASA RPG)
In the late 2370s, in the years following the Dominion War, the Kinshaya renewed their aggression against the Klingon Empire. They started out by conquering the Kreel and absorbinng their resources.
Despite their efforts, the Kinshaya still remained little more than a nuisance. In 2380, the newly aggressive Kinshaya engaged in several acts of piracy in the Empire's Mempa sector and had taken to kidnapping Klingon officers and not allowing them to die. (TNG novel: Q & A)