The indigenous Men of Eriador were absorbed by the civilisation of Arnor.By the time of Valandil this mixed population was diminished and there was not enough people to maintain all the places built by Elendil, until eventually Arnor was split into smaller realms. However when the Hobbits came to Arnor, Númenóreans, allies and enemies were numerous. The Númenorean element was stronger in Arthedain and thinner in Rhudaur until utterly failed. Eventually Angmar was populated by evil men gathered by the Witch-king.
The indigenous Men were also absorbed in the South Kingdom of Gondor, which pursued an expansionist policy. Gondor's borders were extended by the Ship-kings, subduing the pre-Númenóreans. Their blood was mixed and in the following generations the Dúnedain's power and wisdom was diminished.
Hill-men practiced magic and from the 14th century on, fortified the hills of Eriador with dark structures harassed Rhudaur until an evil lord, allied with Angmar, seized its throne and eventually all of Rhudaur was occupied by evil Men subject to Angmar. The Dúnedain were either slain or fled west. The Angmar War however caused those populations to perish. Cardolan was also deserted and could not be repopulated. Rhudaur came to be inhabited only by monsters. After the Great Plague, Minhiriath was deserted except for hunters in Eryn Vorn. Other known Mannish settlements included only the Bree-land and the Lossoth in the far North.
As Gondor expanded East and South, the few remote Dunlendings resisted the Númenórean influence and Enedwaith had no such settlements, other than Tharbad. They remained unaffected, independent and even unfriendly to the Dúnedain, holding their own manners and Dunlendish language.However the Dunlendings also remained hostile to those with Orc-blood. The Dunlendings also dwelt alongside the Stoor Hobbits during their Wandering Days and the latter even formed a related language to theirs.
The Dunlendings suffered from the Great Plague less than other peoples owing to their isolation and were still found in the foothills of the Misty Mountains. By the time of the Ruling Stewards they ceased to be subjects of Gondor and, being surrounded by barbarous folk, they moved to settle the region of Calenardhon as its people dwindled during the Watchful Peace.
In T.A. 2510 Calenardhon passed to the Northern Eotheod who came from Rhovanion and were viewed as usurpers by the wild hill-men and Dunlending herd-folk. Kings Brego and Aldor drove the Dunlendings out of Rohan beyond the Isen until Enedwaith. As the ensuing enmity did not concern the Stewards, the Dunlendings kept hostilities to the Rohirrim and attacked whenever the latter were weak or in trouble.
After the death of King Aldor, and as Isengard became more friendly to them, the Dunlendings passed and settled northern Westfold, the mountain glens around the Ring, and southern eaves of Fangorn, becoming openly hostile. This allowed the two peoples to mingle in some peaceful circumstances; and the dark-haired Landlord Freca was said to have Dunlendish blood When it became clear that the raiders were coming from near Isengard, in T.A. 2710 King Déor led an expedition to the north. He found and defeated a host of Dunlendings, but discovered that Isengard was held by hostile forces.
Freca's son, Wulf, allied with the Corsairs of Umbar who were in turn stirred by Sauron, keeping safe his properties at Adorn. Joining his kin from outside of Rohan with enemies of Gondor that had landed in the mouths of Lefnui and Isen, Rohan was invaded from the East, the Isen and Isengard, finally losing Edoras. Gondor, fighting Corsair fleets, could not help. The usurping Dunlendings were reduced after the Long Winter and finished off by Fréaláf. The Rohirrim now kept a strong force in north Westfold.
Eventually many Dunlendings were found later in the West-March, until again Folcwine, aided by Gondor, reconquered it. But the people remaining between Isen and Adorn were largely of mixed blood, and not loyal to Edoras.Before the War of the Ring, Saruman found in those peoples an opportunity for creating crossbreeds of Orcs and Men. The Dunlendings allied with him and joined his forces in the Battle of the Hornburg. After the War, under King Éomer, there was relative peace.