The curse of Isildur...

[Eomer of the Rohirrim]

Here's an old thread!

Birdland's suggestion is an interesting one. Perhaps Isildur had no power, rather it was the Oathbreakers themselves whose guilty consciences forced them to stay in Middle-earth as ghosts. However, I never get the feeling that the Oathbreakers felt guilt. I have the impression that they wanted to rest in peace, and that they agree to fight in Aragorn's campaign for purely personal reasons.

This would mean that some power other than their own was holding them back from their long rest. And what I've been wondering about is Isildur's power in this situation.