Why did Sauron fear Aragons coronation?

[Inziladun]

Originally Posted by Aiwendil

Possibly. But Aragorn was also the Chieftain of the Rangers; and even if Sauron had no idea that an heir of Isildur was alive, he must have been aware of the existence of the Rangers of Arnor. So it may be that the traps Aragorn refers to were set merely against the commander of the northern Dunedain, with no particular thought that he might be a claimant to Isildur's throne.

Would Sauron really have been that concerned about the Rangers, though? It doesn't look like he had any regard for Eriador in the Third Age, until he learned that was where his Ring had probably been taken. And if he or his servants knew of the Rangers, he should have observed they were guarding the Shire, and he shouldn't have been so clueless either about the location of Hobbits there.