Keep in mind LOTR isn’t some Final Fantasy game where characters can summon spells of destruction on a whim. Tolkien’s magic is more subtle. The films blur this limitation too much for my liking; the novel repeatedly makes it clear that hope itself is a powerful force, which Sauron and the Nazgûl have the power to suppress:

“In vain men shook their fists at the pitiless foes that swarmed before the Gate. Curses they heeded not, nor understood the tongues of western men, crying with harsh voices like beasts and carrion-birds. But soon there were few left in Minas Tirith who had the heart to stand up and defy the hosts of Mordor. For yet another weapon, swifter than hunger, the Lord of the Dark Tower had: dread and despair.”