Arthedain's early chance

[Sophia the Thunder Mistress]

As for the question of population. There can be little doubt Arnor was originally the more populous and advanced of the two kingdoms, why else would Elendil have chosen it for his seat?

I think some weight should be given to the personality of Elendil, when speaking about his choice of seat. Elendil had been among the Lords of the Faithful in Numenor, he'd spoken to and had friendship with the Eldar of Eressea. I think it's only a natural conclusion that Elendil would go to the North Kingdom and maintain contact with the Elven Lords in ME.

In fact, I think it's probably this fact that led to the 'split personality' in the Numenorean realms. The Numenoreans as far back as Aldarion had had dealings with Gil-Galad in Lindon. I would guess that certainly Elendil's original intention was to found a kingdom where the elven speech was spoken, where the Edain could have fellowship with the firstborn. That kingdom was Arnor.

The establishment of Gondor, perhaps, was due to the pride of those survivors of the downfall who still had great pride in Numenor. They chose to make their home near the great Numenorean relics in ME, the globe of Pharazon and so forth. They kept Elendil as their Lord however, which caused the great inconvenience of how to rule two geographically distinct kingdoms, a problem I don't understand without this split. Why would Elendil found two kingdoms when there was plenty of room for all in one or the other? The basic difference of priority in his people, is the answer I find most easy to accept. The founding Arnorians valued their ties to the Eldar, the founding Gondorians valued their ties to Numenor.

If Elendil at heart was one of the Arnorians, it is only natural that he would place his capitol there regardless of population.

Sophia