Land of Oz/WMG

For the film, see The Wizard of Oz.

For Wild Mass Guessing specific to the first book, see The Wonderful Wizard of Oz.

Dorothy and other humans who find their way to Oz are Sliders.
There isn't too much magic in the Mundania portions of Earth, but Fairy Lands are constantly reaching out for those who have "the spark". These individuals become dimensionally unstable, especially when faced with extreme peril. Once in a Fairy Land, such as Oz or the surrounding countries, the ability becomes inactive; it is much harder to leave the Fairy Lands than to enter them.
 * Note that Dorothy found her way into Oz through a tornado, an earthquake, and a storm on the ocean, among other ways. And in one book (Book 5?), she somehow walks into the magic lands without noticing the boundary.

Tim Burton Ships Jack Pumpkinhead with Scraps the Patchwork Girl.
Okay, so a lot of people have noticed how Jack Skellington had striking similarities to Jack Pumpkinhead right? So how come nobody has noted that Sally, a ragdoll and also his love interest, has many similarities to Scraps, even in just appearence alone? Call me crazy, but I think Burton had a case of the ships when creating these characters.

Ozma was reincarnated.
She was the daughter of Pastoria; her fairy heritage didn't come out until later. Thus she is both the daughter of Pastoria and Lurline. Much like Sailor Moon.
 * Interestingly, the author of Wicked and Son Of A Witch (not canon with Baum's works) believes this too, expanding it to include all Ozmas up to the present. Ozma herself stated in the original Baum books that "Ozma" is a title for the female ruler of Oz. Later, it's said that the land is intended for Ozma. Interestingly, she also stated that "Oz" is the title of the male, and it was complete coincidence that the Wizard picked that name. Which leads to...

It wasn't a coincidence that the Wizard of Oz picked that name.
According to Ozma in one of Baum's books, the last true "King Oz" was overthrown by four Witches banding together. Given how Death Is Cheap in Oz when it is possible at all, the traditional way of getting rid of enemy spellcasters is to remove their memory and banish them. This happened to King Oz. But it's not that easy to erase a fairy, especially if the land is as dedicated to him as it is to Ozma. So, possibly through Reincarnation, Oz shows up in... er... Oz again, but as a weak shadow of what he was. Glinda allows it for a time to see what happens; after encountering Dorothy, he leaves. He comes back in a later novel, and Glinda takes him as an apprentice. Notice how strange this is: Glinda and Ozma are very paranoid about anyone but themselves practicing spell magic, and yet they're allowing the same man who overthrew Ozma's parents to do it. If his presence in the land cannot be removed, then he will be kindly controlled. Plus, it's possible that the land needs Oz and Ozma, which leads to...

Ozma is a Fisher King. (Fisher Queen?)
When she wasn't on the throne, the magic of Oz was weaker. When she regained the throne, the inherent magic of the land strengthened. Hence anything later that contradicts earlier books, well, that was Ozma's influence having been weakened by not being on the throne.

All of the Above and then some

 * 1) Lurline was one of the Fair Folk, who retreated to an otherwise desolate Nonestica with her Fae Court when she saw the world of humans was going to run them out. However, multiple cracks in the fabric of reality remained.
 * 2) The "humans" of Oz are actually human/Fae hybrids of varying degrees (much like the D'Angelines are of angel and human descent), descended from humans that either fell through the cracks of reality or were taken in by the Fae.
 * 3) The Fae blood explains how they can use magic in wildly varying degrees. It also makes them hard to kill, and longer-lived, almost to the point where an outsider would think they're immortal.
 * 4) The secular citizens of Oz believe Ozma is a descendant of Lurline. The Lurlinist faith beleives she is a reincarnation. The answer is "some of both" - There is a part of Lurline's lifeforce that is passed from mother to daughter upon the old Queen's death. (Thank Tin Man for this one)
 * 5) The inqusition and troubles of Wicked happened, but not quite in the way Maguire depicts. Munchkinland didn't splinter off, but it was pretty much not communicating with Oz, either.
 * 6) The "Emperor Apostate" from Son of a Witch and A Lion among Men was overthrown and killed by Jinjur's revolt. The Scarecrow (who actually escape) and Nick Chopper found and restored Ozma Tippetarius to the throne. Ozma immediately put an end to the Inqusition and passed legislation of religious and cultural tolerance, bringing sanity back to Oz.
 * 7) While Ozma held the throne, she needed a goodwill ambassador. Dorothy became Princess part because she was a symbol and champion and otherwise divided population could rally behind.
 * 8) As they became older, Dorothy also became Ozma's consort in all but name.

Glinda "nullified" the Wicked Witches of the East and West after Dorothy incapacitated them.
People can't die in Oz, and this was still in place even before the first book, as the Tin Woodman's original body parts will attest. So, that means while Wicked Witch East was smushed under a house, and Wicked Witch West was a puddle of goo, they were still alive. In later books, Glinda always provides the means to erase the memory and otherwise remove magical ability from threats. What their fate was, none can say, only that they're not coming back...
 * She left the house there and put the Wicked Witch of the West in a bucket. With a lid.
 * The Wicked Witches hadn't kept themselves hydrated. The Wicked Witch of the East disintegrated into dust. (Maybe that's where the original Powder of Life came from!) The Wicked Witch of the West dissolved into the water Dorothy threw onto her; even if she was still alive, she was in an And I Must Scream kind of situation.
 * Then, how do you explain the former Nome King coming back a lot and causing trouble?
 * The first time he was killed, he was in a magical land that wasn't Oz. They didn't take extra care to make sure he stayed dead because they were trying to restore various citizens of Oz to their true forms. So he reincarnated from what rock remnants the egg left behind. He goes by a different name when we meet him again, and he did have amnesia for a while before he caused trouble again. He came back much smaller, too. The next time, they did try a mindwipe...

Each Oz book takes place in its own alternate history
It would explain a lot of inconsistencies like the status of death, history, and Ozma's heritage and God knows what else.
 * There is a book called Paradox In Oz which seems to support this.

The Desert surrounding Oz being deadly is just propaganda
In the Marvelous Land Of Oz, in the chase scene with Mombi and Glinda they eventually encroached onto the Desert but were not turned to sand. The whole deadly thing was just a piece of deceit concocted by the wizard to keep his subjects from developing wanderlust and leaving his domain. Mombi knew because she had past dealings with the wizard, and Glinda knew because she was Glinda the Good. Ozma using a unraveling carpet to cross the desert into Ev was either just so her chariot could be move more easily, or her attempt to maintain the lie as a deterrent to potential foreign invaders.
 * The sand is effective against Wheelers, however.
 * I thought that the desert was just really wide and emitted poisonous vapors? Only birds can fly high enough to get at clean air.

The Xanth books are part of the same universe as the Oz books.
The book Ozma Of Oz shows that there is more then one fairyland in existence. Xanth is another one of them. And, like Xanth, Oz can't seem to decide on a geographic location. In the first two books it is hinted that Oz is located in the deserts of North America. (If true, this would've made life in Las Vegas and in Phoenix, AZ, much harder.) In later books, Oz is part of an entirely different country. Two, Oz seems to have its own region of madness that cause the many inconsistencies.

Dorothy and Trot have innate magical abilities, but they have no knowledge of this.
The books say they were both marked by the fairies. (We get to see Dorothy be marked.) And they both seem to be weirdness magnets. This is because they are both using magic subconsciously. For example, Dorothy when caught in a cyclone, ends up in a beautiful fairyland; when she starts missing Oz, she gets shipwrecked only a few miles away, and nothing seems to be able to hurt her. (That kiss from the Good Witch of the North was good!) Trot wants to meet mermaids; she meets them. Dorothy begins to consider Oz her home; she ends up living there as a princess. And God help Oz and beyond if they become aware of this abilities and get power hungry, it'll be the Wicked Witch Of The West all over again. Also, the various magical devices Dorothy uses throughout the series the silver shoes, the Nome King's belt, the Good Witch Of The North's kiss (I know it's not a object but I don't know what else to call it) are psychological crutches that allow her to unleash her magical whoopass; the objects have some potent powers in their own right, but most of the powers they exibit are just Dorothy subconciosly using magic.
 * You could take this even further: Oz didn't exist until Dorothy created it. She's a powerful reality-warper whose powers unconsciously activate under times of great stress (like, say, when her house is being blown away by a cyclone). That explains why the portrayals are so inconsistent throughout the books, why new characters and lands appear seemingly out of nowhere, and why so many of Dorothy's trips to Oz are precipitated by some kind of traumatic event or natural disaster.

It is all Dorothy's fantasy.
She was unhappy with her life on the farm, so she dreamt up Oz. She became aware of the family's money woes, which resulted in her removing money from Oz. She got lonely, so she dreamt up Ozma as a playmate. Someone she knew died, so she removed death from Oz. She grew to hate life on the farm, which lead to her dreams about moving there permanently!!

The Nome King is Hades, or his avatar.
He is said by the Shaggy Man to possess and control all the treasures under the Earth, which is one of the things Hades gained when he gained possession of the underworld after the war with the Titans. This could justify at least some of his weakness to eggs, which are symbolic of new life and growth, things antithetical to the dead underworld. There seems to be a bit of Satan mixed in there too; the King of Ev made a Deal with the Devil for eternal youth with the Nome King, sacrificing his family in the process. This could also explain why, unlike all the other villains, the main characters can never permanently defeat the Nome King: He is connected to a god, or is one.

Oz is not what it seems.
One, Ozma and Glinda banned the use of all magic besides them and the Wizard, which is quite reminiscent of authoritarion states banning higher education and the reading of unauthorised books in order to stop the citizens from organizing rebellion. Two, Ozma's Magic Picture allows her to see anything in Oz and beyond, which is why the Ozites never criticize the government; they know the empress (Sorry, "Princess.") is watching for thought crime, and Glinda is known to have many spies. Three, everyone is immortal in Oz. After a few centuries of this, can you really call the residents "human?". Four, Glinda seems to like setting up puppet leaders to placate the population and let them think there being represented Soviet Union style.
 * Except from what we see in many of the books, there are whole societies in Oz that Ozma doesn't even seem to be aware of or know anything about until meeting them. In Glinda of Oz, the Flatheads and Skeezers are on the verge of a war, but no one knows this until Dorothy happens to read a single sentence in the Great Book of Records. Ozma openly admits she knows nothing about them except that the name "Skeezer" was on a portion of a map. Glinda tries to use magic to learn more, but can only get a few sketchy details. So the books are quite clear that Ozma and Glinda are far from omniscient.

Ozma was adopted
Pastoria, for whatever reason could not have children. So Lurleen; queen of the faries, gave Ozma to Pastoria to be raised as his daughter. Make sense?

The events of the first two books are an Evil Plan by Glinda.
She had a direct role in removing two of the Wicked Witches (the Wicked Witch of the South in the backstory, and Mombi in the second book), and quelled a revolt by force of arms to install a child ruler that she herself declared rightful, remaining Ozma's trusted advisor. (Riiight...) What does she do in this new position? Assume monopoly on magic in Oz. Yes, yes, she's a "good" witch... take our word for it.

The precedent set in the case Ozma vs. Ojo does not apply to violent crimes.
It would be a real can of worms if it did.

Oz doesn't exist at all. In fact, Dorothy is an innocent girl who suffered horrible trauma after being carried off for miles by a tornado in her farmhouse.
In order to help herself survive, she hallucinated the journey home and her companions actually are parts of her subconscious coming to the forefront to help her cope. After her return, she became convinced that Oz was real. In Ozma of Oz, she was actually taken across the ocean to a sanatorium, but the poor techniques of dealing with mentally ill patients brought out her Oz fantasies. She assigned different roles to people she met there, and since she was very charismatic the others began to believe they were these people. She was transferred to different locations - one in California, one in the Midwest - but finally it was decided that she would remain in an institution in Kansas, which is why she imagines she stays in Oz after book six. She continues to convince patients they are her companions, but the doctors don't stop her because she rarely causes any real trouble, in fact keeping order among the more violent patients. The impenetrable desert is actually the gate of the asylum.
 * Wasn't that what led to the events in the movie Return to Oz?

The whole story was actually about Dorothy's time as a Green Lantern
Her predecessor named Glen-Daa brought her onto her ship in a beam that resembled a tornado. Her first act with her power ring was to form a house and smash it over a dictator that Wetch was sent to take care of, accidentally killing her in her desparation to make her go away. She met three other new recruits whose alien appearances led her to call them by the familiar earthly things they most resembled, a scarecrow, a tin man, and a lion, and together they went to Oa to fully learn their new duties as members of the Green Lantern Corps. Dorothy and her three new friends were then sent by the Guardians to deal with another dictator named Wikid Wess on planet Win-Ki. Again, Dorothy accidentally killed her, this time with a bucket of water. Ashamed of killing two people and missing her family, Dorothy asked to be stripped of being a Lantern and to be sent home, despite the insistence of her friends that it was an accident and that she deserved another chance. Later, she told her story to a man named L. Frank Baum who wrote it down, taking some liberties (such as changing Oa to Oz, making the Guardians one man called "the Wizard" and making him a fraud, lowering Dorothy's age so that younger readers could identify with her, etc). The later books had nothing to do with Dorothy's story and were purely from Baum's imagination. Kind of lame, but the idea's been eating my brain all day. Baum really did make Dorothy so young to attract younger readers to the character, by the way.
 * If that's the case, give Nick Chopper a Star Sapphire! He's motivated by love every step of the way. He was cursed because he fell in love with the Witch's servant. He kept working despite the curse because he was so besotted he didn't care about the consequences. He desired a heart to win her back, and went on a quest in the 10th book to try and find her. (It didn't end well for him).

L. Frank Baum is Oz.
Or he was, anyway, before be carried back in Omaha in his balloon, where he found his family again, and that he had now a granddaughter named Dorothy. He never told any adults about his adventures, but only Dorothy, who listened to the stories with her little terrier, Toto. Naturally, Baum decided to later on convert these into text, while telling them from the perspective of one little girl who had come into his kingdom and indirectly set him back home, and he inserted Dorothy and her little dog for into them for the sake of his grandchild's amusement. He later wrote other novels of Oz because Dorothy still liked them, even as she got older.

Tollydiggle's "fierce temper."
Omby Amby's wife has "a fierce temper," right? But yet, it's later revealed that he's married to Tollydiggle (the very nice lady who runs the Emerald City jail). So Jack Snow goofed, right? Not at all. Tollydiggle is a very nice lady, and she's got a long fuse. But...let's say she were to run into the First and Foremost. I'd almost feel sorry for him.

The canonicity within Oz is questionable in universe.
The high magic radiation causes reality to shift on an unprecedented scale within Oz. The reason Oz hasn't been around since Baum died (or since the last post-Baum book that didn't use the Literary Agent Hypothesis) is that the Land of Oz RetConned itself into a fictional existence, and being fictional, no longer has the power in our universe to retcon our universe into having it again. Supposedly reliable informative figures are considered reliable not because they know more, but because they float on the tides of Oz's changing history, having a greater tendency to remember what currently is rather than what they originally learned. This is supported by (or possibly just explains) the scene in Wicked where the records are horribly inconsistent; they're mostly inconsistent because they're the most stable archive of information, not because they're intentionally wrong.

The Wizard is a Secret Service agent like Jim West and Artemus Gordon
He arrives in Oz about 30 years before 1902, which puts it right during the Grant administration. He's a master of disguise, an inventor, and can apparently talk just about anyone into anything. Obviously Agent Diggs (his real last name, as revealed in Dorothy and the Wizard In Oz was sent to Oz by the government.