Well, I think we can assume that the bridge at Tharbad was reconstructed, and it was once again an inland port facility.
Tolkien tells us that Annúminas was rebuilt, so the idea that there was a vice-regent or governor chosen from one of the northern Dúnedain is a good bet. No mention is made of the reconstruction of either Fornost or
Amon Sûl, but given the importance of those sites in
Arnor’s history, they were probably rebuilt. Technically,
Imladris would have fallen under the political control of
Aragorn Elessar after the departure of
Elrond, but since Elladan and Elrohir apparently lived there for some time (as
Sam told his daughter Elanor in the “Epilogue” in
Sauron Defeated), it is unlikely that Aragorn exerted any undue influence there: Elladan and Elrohir and the remaining Eldar of Imladris were important allies, and as far as the northern Dúnedain were concerned, Elladan and Elrohir were peers of the
realm. The importance of the place at the western end of the High Pass of the Great East Road over the
Misty Mountains made it strategically important. The same would be true of
Lindon and its port facilities: as long as any Eldar remained there, it is unlikely that the Dúnedain would try to exercise any political influence.
Bree no doubt became once again an important town in the North.
The Shire was the ancient royal demesne of Arnor, and in effect, reverted to that position under Aragorn with the Mayor, Thain, and Master of
Buckland as his royal governors. The Tyrn Gorthad region (the barrow-downs) and Minhiriath between the Brandywine and the Greyflood had previously been the most populated
regions of Arnor, if I remember correctly, and over the next couple of centuries, might have once again been more thickly settled.
There is no reason to consider Arnor a backwater, although the folk of
Gondor might have been taught to think of it that way: that idea seems to have been planted when Arvedui made his claim on the throne based upon his marriage to Fíriel daughter of Ondoher at the end of the second millennium of
the Third Age, and was repeated in bitterness by
Denethor at the
Stewards’ mausoleum in Rath Dínen.
Moreover, Aragorn was born
King of Arnor, even if he only took the title Chieftain of the
Dúnedain of the North. When he was crowned
King of Gondor, he was wearing the Star of the North on his brow as the royal
symbol of kingship, and so at that point, he became king of both
kingdoms, rather like the first pharaoh of Egypt, variously either Menes or Narmer, who combined Upper and Lower Egypt from two kingdoms into one and who wore the Double Crown combining the Red Crown of Lower Egypt and
the White Crown of Upper Egypt. This seems to be reflected in the symbol of Aragorn wearing the Star of the North (not a physically tall symbol, rather like the Red Crown) and the high
helm of Gondor (which Tolkien drew in one of his
Letters and looks rather like
the old White Crown).
And since Aragorn was born King of Arnor, it is reasonable to assume that he took some pains to see to it that part of his realm was restored as well as possible because it represented his royal heritage and unbroken claim to be King of the
Númenóreans in
Middle-earth.
).
