I can't give you the
dates off the top of my head, but...
at a point in
Arnor's history it broke into three
realms (sibling rivalry among the princes): Arthedain, Cardolan, Rhudaur. Some centuries passed and the line of
Elendil failed in Cardolan and Rhudaur, so that at some point the king of Arthedain tried to reclaim the rest of the lands as his kingdom (since he was the sole heir of Elendil). Of course his claim was rebuffed. It was the king of Arthedain that gave the
hobbits permission to settle in
the Shire (T.A 1601).
At the same time the
Witch-King of Angmar (who was the chief of the
Ringwraiths, though no one knew that at the time) set up a
realm in the northern ranges of the
misty mountains, that encompassed both sides of the range. It was an
evil realm, of course, with
trolls,
orcs and evil
men, and it fought the remnant of Arnor (Arthedain, and to a lesser extent Cardolan -- Rhudaur had become evil and allied to
Angmar) bitterly. At the same time
Gondor was facing some fierce enemies of its own, the Balchoth (a people from
the east) and the
Haradrim. Realizing that an evil power, guided by a fierce hatred of the Dúnedain, was directing the attacks, the two realms struck an alliance. In T.A. 1974 (I think) the last king of Arthedain, Arvedui, sent a message to Gondor that Angmar was rounding up a massive force and requested help. But before any help came, the
Witch-King's
armies overran Arthedain. The king was forced to withdraw to the northern waste. While the Angmarians (?) were feasting, a fleet arrived at
the Grey Havens, coming from Gondor. Gondor was at that time much stronger than any realm in the north, and the small force (in the
Gondorians' reckoning) was enough to rout the Angmarians. But in these
battles the last kingdom of the North came to its end, as Arvedui was lost in the sea and the area became really an underpopulated wasteland. Only in the Shire and in
Bree there were enough people.