Rhudaur was the smallest of the kingdoms originated from the break up of Arnor (861 T.A). The other kingdoms were Arthedain and Cardolan.
Right from the start of its existence it was unfriendly against the two other successor states and had a bitter conflict with Cardolan over the tower of Amon Sűl and the Palantir associated with the tower.
The history of Rhudaur is largely unknown, except that the last Kings owed their position to Angmar and were its vassal and thus enemies of Arthedain.
Angmar terminated the kingdom in 1409 T.A.