The Dunlendings were a dark-haired and dark-skinned group of men who inhabited Dunland. They were remnants of an old race of Men who at one time lived in the valleys of Ered Nimrais or the White Mountains. They were related to the Dead Men of Dunharrow and also the Breelanders, especially notable in this regard is the 'squint-eyed southerner' which the Hobbits encountered in Bree.

The Dunlendings first appeared toward the end of the Second Age and they felt that their lands extended into the lands of Calenardhon. When those lands were given to the Rohirrim, they became angry and have fought ever since with the Horse-lords and the people of Gondor. They hated the Rohirrim because of their battles over land and because Helm Hammerhand had slain their leader Fr├ęca before the Long Winter.

The Dunlendings mostly feared the Rohirrim and the Kings of Gondor, but when the line of kings failed and whenever the Rohirrim were weakened, the Dunlendings would attack and try to invade the lands of Rohan. When Saruman came to Isengard and eventually turned to the shadow, he enlisted the help of the Dunlendings against the people of Rohan for he knew of their long standing feud.

After the War of the Ring the Dunlendings were pardoned for any wrongdoing and they were given Dunland for their own, and they never tried to expand upon their borders after that.
Encyclopedia entry originally written by Nienna-of-the-Valar