As with a lot of things the back story is actually as interesting as the show.
There is an idea that the book contained an allegory of the late 19th-century bimetallism debate regarding monetary policy. At the beginning of the novel, Dorothy is swept from her farm to Oz by a cyclone, which was frequently compared to the Free Silver movement in author's time. The Yellow Brick Road represents the gold standard and the Silver Shoes (changed to ruby in the film) which enable Dorothy to travel more comfortably symbolizes the Populist Party's desire to construct a bimetallic standard of both gold and silver in place of the gold standard. She learns that to return home, she must reach the Emerald City, Oz's political center, to speak to the Wizard, representing the President of the United States. While journeying to the Emerald City, she encounters a scarecrow, who represents a farmer; a woodman made of tin, who represents a worker dehumanized by industrialization; and a cowardly lion, who represents William Jennings Bryan, a prominent leader of the silverite movement.
The villains of the story, the Wicked Witch of the West and the Wicked Witch of the East, represent the wealthy railroad and oil barons of the American West and the financial and banking interests of the eastern U.S. respectively. Both these groups opposed Populist efforts to move the U.S. to a bimetallic monetary standard since this would have devalued the dollar and made investments less valuable. Workers and poor farmers supported the move away from the gold standard as this would have lessened their crushing debt burdens.
The Populist party sought to build a coalition of southern and midwestern tenant farmers and northern industrial workers. These groups are represented in the book by the Good Witches of the North and South. "Oz" is the abbreviated form of ounce, a standard measure of gold.
This allegory appears to be bollocks however.