A major theme of The Return of the King is that evil often destroys itself in the face of goodness and that powerful evil is short-lived. Tolkien shows how traits such as selfishness, greed, violence, and pride internally sabotage the forces of Mordor in time, while the kindness shown by the Fellowship helps them to succeed against all odds.

Several times in The Return of the King, Sauron’s forces are defeated because their tactics unintentionally help the forces of good. The first example of this comes when Sauron sends a cloud of darkness to terrify and demoralize the men of Gondor. However, Éomer realizes that it will help them to slip past the Orcs guarding the road unseen, saying “The accursed darkness itself has been a cloak to us. And now, lusting to destroy Gondor and throw it down stone from stone, his orcs have taken away my greatest fear. The out-wall could have been held long against it. Now we can sweep through” (816). Similarly, Sam is able to rescue Frodo because the greed and violence instilled in the Orcs of Mordor causes them to fight each other. While Sam never could have killed all of the Orcs guarding Frodo, they kill each other in a fight over the mithril shirt.