Act 1: The Wizard (he should never have a name) crashes into Oz. He begins to use his knowledge to help and dazzle people. He glues china people. He pulls coins from people's ears. He touches fire to a powder and unblocks a river. His legend grows and Oz has been without a leader for a long time. It's been years since Ozma was on the throne. And through a growing consensus, the Wizard gets put in charge.
Act 2: The witches of the North, South, East, and West come to meet this Wizard. They can see that his power is nothing like theirs, but some of the things he does is just a powerful. The Witch of the North leaves, not wanting anything to do with him. The Witch of the East chooses to consolidate her power in Munchkin land. The Witch of the West tries to steal the source of his power, but ends up hurt and she joins with her sister in the East to recover. Glinda, Witch of the South, chooses to join with the Wizard because she believes that Oz needs a leader.
Act 3: The armies of the East and West march on the Emerald City. The Wizard uses science and illusion, and a little bit of Glinda's magic, to defeat the armies. With the battle won and the witches retreating to their homes. The Wizard is declared The Wizard of Oz and the movie ends.
Hell, that could make one good movie or a pretty decent trilogy. Oh the lost opportunity.