Ever heard of Armageddon? The end of the world--the final battle between good and evil. Narnia has its own Armageddon in The Last Battle. Aslan's roar is all it takes for Narnia to come to an end. It's not a time-consuming, horrid end; it just takes a few moments for all the beauty of Narnia to disappear. It's something Peter, Edmund, Lucy, Eustace, Jill, Digory, and Polly were all able to watch, but, obviously, they couldn't be in Narnia when it happened, or they, too, would have been destroyed.
All it took was the roar of the Lion. None of the great kings and queens and other characters of Narnian history did anything.
Let's look at our own Armageddon, or Har-Magedon, as may be a more appropriate spelling. The armies of the earth assemble, ready for the ultimate battle between God and the Devil. The armies march, the battle is about to begin, and, BOOM!, it's over. God does all the work. We don't even do anything. Just as Aslan's roar brought the end of the world of Narnia, God brings about the end of our world...when the time is right.