[Knight of Gondor]

The appendices of RotK speak of the remaining evil creatures that had to be routed out and killed by King Aragorn and King Eomer. The ruin of Mordor was left alone, lest any of the evil that dwelt there be disturbed, or something like that. That's one of the things that always bothered me a little about Middle-Earth...you never do defeat the evil entirely. Morgoth came back from being chained, then Sauron stayed after Morgoth's exile. Then Sauron was destroyed, but wasn't fully gone. Then he was finally destroyed...well, we don't know much beyond that.

I agree, though, the primary evil after Sauron's fall was in the weakness of Man.