Quote:
For at Erech there stands yet a black stone that was brought, it was said, from Numenor by Isildur; and it was set upon a hill, and upon it the King of the Mountains swore allegiance to him in the beginning of the realm of Gondor. But when Sauron returned and grew in might again, Isildur summoned the Men of the Mountains to fulfill their oath, and they would not: for they had worshipped Sauron in the Dark Years.
'Then Isuldur said to their king, "Thou shalt be the last king. And if the West prove mightier than thy Black Master, this curse I lay upon thee and thy folk: to rest never ubtil your oath is fulfilled. For this war will last through years uncounted, and you shall be summoned once again ere the end." ' -from 'The Passing of the Grey People' from RotK.
He was King of the Men of Ered Nimrais (of the White Mountains) these oathbreakers were probably kin of the Dunlendings.