The Resurrection of Arnor

[Gwaihir the Windlord]

How did Aragorn suddenly bring Arnor back to life again? The sparse inhabitance of Rangers would hardly have been enough to repopulate it; presumably he took a gathering of colonists North from Gondor, but would that have been possible straight after the War? It was said then that Gondor was sorely underpopulated. It grew again and became as full as it ever was, but that would have taken many years. It had to recover itself before it had the resources to restart the North-Kingdom. It appears that Arnor sprang back into existence shortly after the defeat of Sauron.
Rohan was well-populated. They would have sent a lot of men, but Arnor would have had to be mainly recolonised from the Numenoreans, Gondor, rather than the Northmen of Rohan.