Good vs Evil

The Fate of the World
One story that can come out of White Box play is an epic good verses evil struggle where the fate of the world hangs on the outcome. I think of this as the Tolkien tradition. I love Tolkien, hobbits, Middle Earth, all of it, but the Tolkien Tradition is only one possible way to approach White Box play. White Box was written by gamers with a wide span of interests in history, and fiction and it was written to be able to play all of it. From the morally ambiguous historic crusades to the purity of Tolkien, White Box is first about world creation, what the authors called milieu.
Before play begins, even before any characters are created, the referee must build a world or setting for the coming action. Traditionally this has often been a dungeon, which has the advantage of being a very tightly defined setting not likely to get away from its designer; stone walls tend to limit options. But not all dungeons are alike beyond that point. Some are places of evil, some are not. Some are places of mystery, magic and treasure. Some are big puzzles, some tests, some playgrounds or underground amusement parks. The dungeon can be a floating spaceship, a pocket dimension or dreamland, or the sewers under a modern city. Imagination is the only real limit.
Going back to Appendix N (Dungeon Master's Guide) one sees the sources Gary Gygax listed as inspirations for the game. Through the Little Brown Books, Mr. Gygax and Mr. Arneson introduced the world to a new way to enjoy gaming, but also a new way to enjoy literature. Fantastic stories have been a part of our collective culture (often intermixed with religion) since the beginning. The LBBs give us a new way to experience those fantastic stories as we play out our tabletop adventures, chronicling the deeds of our imaginary heroes. Just what those stories will be is a cooperative endeavor between referee, who defines what the story is likely to be about and players who determine what the outcome will be.
Many game milieux have been created by drawing heavily on a setting found in a book. I wonder at the number of Hyborias and Middle Earths that have been re-created for game use. I myself have used each as a setting for at least one campaign and there are many other popular fantasy sources from which to draw inspiration. Today's referee can download a setting, pull one off the shelf of a local hobby store or create their own, drawing on whatever inspiration suits them.
Regardless if it is borrowed or invented, the referee sets the milieu and therefore determines what is in the shared imaginary world, who the protagonists are, and what conflicts exist. The rest is largely up to the players who control the main actors, the PCs. Epic good verses evil is a choice the referee may make, but unless the PCs take an active role, that may not be the story that develops. What if the hobbits decide the one ring is not their problem? Railroading is seldom a good choice considering everyone's enjoyment. However, by not taking care of the one ring, evil may win out and the PCs will have that to deal with...eventually.
Much of the fantastic literature which appears in Appendix N is way less a story of good verses evil than Tolkien's Lord of the Rings. The sword & sorcery tales, of which there are many listed in Appendix N, generally lack this dichotomy. Often they are complex tales of heroes and anti-heroes who struggle with moral issues much as we in the real world do. Magic is often portrayed as dangerous stuff beyond man's understanding and ability to control. Occasionally the tales are of hopeless futility where humanity has no chance against the horrors that lurk just beyond. Any and all of these imaginings can be the focus of a White Box campaign.
How dark and desperate the milieu is, what role magic plays, how does faith come into the story? These and many other decisions are made before the first PC ability score is rolled. The epic struggle of good verses evil, where the actions and decisions of a handful can make a very real difference that effects the future of all of mankind can be a very satisfying fantasy. We would all like to think our actions have real meaning, that we can change the world for the better and that good triumphs over evil. (Some of us would just like to be able to reliably tell good from evil.) Therefore it seems no surprise such stories are popular fare, inside gaming and out.