[Mithalwen]

I think that Tolkien's feelings about industrialisation might have given him scope for evil in the later ages of Middle Earth - expanding on the microcosm shown in the scouring of the shire. But you might have needed a bit of a time delay... I think it would have devalued the triumph of the War of the Ring if a mjor threat had arisen too soon. However in the apppendices it does refer to Eomer and Aragorn fighting together again in a "mopping" up exercises in the south. However I don't think there is a personnage in the books that would have the power to "face up" against Aragorn at the height of his power.