You could say the populations of the three kingdoms withered away over the centuries. Rhudaur was apparently only sparsely settled by the Dunedian but there were hill-folk living there. I get the impression these were primitive men, probably descended from Easterlings who served Morgoth in the First Age and were not very friendly with either the Elves or the Edainic peoples of Eriador and Rhovanion. Tolkien doesn't tell us anything about them, except in one place he says they became sorcerors (possibly a rejected text -- I don't have time to check). Some people have speculated on whether they might be related to the men of Angmar, who lived on both sides of the Misty Mountains. These, too, were probably descendants of Easterlings who once served Morgoth.

[I should note that an alternate theory holds the hill-folk of Rhudaur may have been an eastern branch of the Gwathuirim, distantly related to the Dunlendings and Breelanders.]

The Dunedain of Rhudaur dwindled, probably most died during the centuries of intermittent strife between Rhudaur and Cardolan from 863 to circa 1300. The decline of the Dunedain, and the failure of the Isildurian house there, led to the overthrow of the kingdom by a hill-lord whom Tolkien says was in league with Angmar (probably around 1350). The remaining Dunedian were then hunted down or driven out of the country. Rhudaur was defeated in the war of 1356 but its hill-folk apparently survived until the war of 1409, when they were utterly destroyed (wiped out by the Elves, it appears).

Cardolan was more heavily populated than Rhudaur. Of course, there was Tharbad on the Gwathlo itself which probably served as the capitol city of the kingdom, but there were many Dunedain in the South Downs (which extended almost all the way to Cardolan). We have no information on whether these Dunedain lived in towns, cities, or scattered farms and estates. Their lands were overrun in the war of 1409. Those who didn't perish retreated westward to the fortified hills of Tyrn Gorthad, but even there the last prince was finally overcome.

The rest of Cardolan's people were probably descendants of Gwathuirim and Beorians, mingled with Dunedain. They must have withdrawn before the onslought of Angmar and Rhudaur in the war of 1409 as well. It would be reasonable to assume that many people fled to Tharbad and that others would have sought refuge in the lands of Minhiriath (the lands between Gwathlo and Baranduin). But these people mostly died out in the Great Plague of 1636.

Arthedain survived the wars of 1356 and 1409, and it survived the Great Plague. But the grant of the Shire to Hobbit colonization in 1601 shows clearly that Arthedain had suffered a significant loss of population, probably due to the fact that Annuminas had long been deserted (probably since the 3rd century, after Valandil's death). We don't know how important Bree was at this time but it was apparently much larger than at the end of the Third Age, if for no other reason than that there was a large Hobbit population there.

Hobbits had at first settled in Rhudaur, but with the rise of Angmar around 1300 they began migrating west and many settled at Bree. Tolkien implies there were other Hobbit communities (and probably other mannish communities) in Arthedain as well. My guess is there must have been one or more towns between Bree and Fornost Erain and probably several towns in the lands between Baranduin and the Weather Hills. These towns would all have been diminished or disappeared completely in the Great Plague, or were abandoned by the Hobbits when they migrated west to the Shire.

Arthedain's population apparently recovered after the Plague, however, because Araval tried to reoccupy Cardolan (he reigned from 1813 to 1819). He fought a war with Angmar in 1851 and the comment about the failed recolonization of Cardolan occurs after that, so it may be that the attempt occurred after the war of 1851.

The final war with Angmar lasted some years, and apparently drained the strength of the Dunedain. Arvedui must have lost many men in battle before the winter of 1974 when Angmar overran the kingdom. It would have been at this time that all remaining towns beyond Bree (if there were any) vanished for good, and undoubtedly a large part of the population perished. Of course many people found refuge in Lindon, and probably a lot of people fled south through Sarn Ford and took refuge in Minhiriath.

By the time Angmar was destroyed, there were basically only four populations left in Eriador: the scattered Dunedain, the Hobbits of the Shire, the Men and Hobbits of Breeland, and the few men still living in Minhiriath. Of course there were Elves, but we don't really know what their circumstances were.

The Hobbits obviously flourished in the next thousand years. The Shire grew and the Buckland was founded, but the Bree men seem not to have flourished. Tolkien mentions no colonies like the Buckland. There is, of course, the mysterious Forsaken Inn a day's journey east of Bree. Why was it there? To whom did it belong? And was there a town or village around it or nearby?

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