So Sauron is defeated, Mordor is emptied, then the Wizards are sent down some time later? Some humans take up a bit of residency in/near the western Mordor mountains to keep watch. But they are apparently driven out thousands of years later by evil and don't raise any alarms. Along with the Wizards, couldn't Eru also send down some magical spirit that would have transformed Mordor into a beautiful, fertile land that people would enjoy living in and evil would flee? How about the Elves planting a forest in Mordor and living there?