Some events in history seem to change how people think. Some of these events are in your face like the events of 9/11/01 or world wars etc., while others are more subtle like the moon landing or even Caption Kirk kissing Lt. Uhura on network TV. They change the way people see the world and by doing so change the world like that REM song, "it's the end of the world as we know it / I feel fine." The more I learn about the Chicago World's Fair in 1893, more I think that this maybe one of those events. One in four Americans attended this event. Think of that for a minute. This was an era where the train was the fastest mode of transportation. This was a huge event. Hamburgers, cream of wheat, chocolate bars, Ferris wheels, chewing gum, pancake mix, hula dancing and ragtime music (by none other than Scott Joplin) were introduced to the American public. It made some heads spin.
Frank Baum was a middle-aged man when he attended this event. It was a game changer for him. He was an author and an unsuccessful businessman. He wrote about raising chickens and published a trade journal about the subject. A few years later he published The Wonderful World of Oz. Among other things, the Emerald City had incredible inventions like color televisions, laptops and wireless phones. His Oz was an incarnation of the Chicago World's Fair.
A few other things I learned about him is that he grew up in up-state New York State not far from the original Yellow Brick Road: http://www.bethlehemfirst.com/yellowbrickroad/.
He based both the good witch and the bad witch on his mother-in-law, Matilda Joslyn Gage, who was a big name in the woman suffrage movement. She and her friends were also interested in witchcraft so the connection wasn't a big leap. She was a nag to him but she also was the biggest supporter of his writing and urged him to put his stories in print. Ironically, she was also a big advocate for Native American rights. Baum's other claim to fame, later in his life, was publishing some scathing verbal attacks on plains Indians in the Aberdeen Saturday Pioneer provoking fear and urging their extermination. He did this mostly because he was broke.