The Northern Kingdoms

[Inziladun]

Originally Posted by Belegorn

I think maybe their histories would have followed basically the same arc except for some of the more noble houses, where in Gondor they started to become subject to mating with Middle Men, in Arnor and afterwards they tended to keep it in house. Of course few houses remained relatively pure in Gondor and even from the nobles of Dol Amroth one of the women, Morwen, married a Rohirrim and we have Thingol, his sister, and their 3 children. Eventually 2 of their descendants did marry back into the high houses in Gondor, Éomer with Imrahil's daughter, and his sister Éowyn into the Steward's House with Faramir.

It seems to me that the very blood-purity that set Arnor apart from Gondor, and ultimately resulted in the return of a king that would rule both kingdoms, was also what hastened its initial fall.
Gondor's intermingling with the lesser Men of Middle-earth gave it the manpower to stand as a bulwark against Mordor and its allies even after such calamities as the plague and the Kin-strife, whereas the Witch-king went north and simply wore down Arnor over time through attrition.