Okay, there is a lot of symbolism in Wiz of Oz, to say the least, and I am by no means an expert, but here goes with a few. An internet search could almost certainly pull up more/different answers.
Kansas = Great Plains (dry and dreary-remember, the first of the movie is not really Black and White, more of a brownish haze covering everything.)
Dorothy = your everyman (something always in the way of their dreams)
Scarecrow = Farmers (intellectually challenged)
Tinman = Factory workers (they can't get him going without oil)
Lion = WJ Bryan (seems strong, but actually a coward)
Wicked Witch of East = Eastern Industrialists/Bankers
Wicked Witch of West = Railroads
Flying Monkeys = Plains Indians (just listen to them as they fly off)
Oz = Eastern US
Emerald City = D.C.
Wizard = William McKinley
Yellow Brick Road (Gold Standard)
Silver Shoes (unlimited coinage of silver- on the Populist Platform) The shoes are not ruby in the book.
Munchkins = maltreated Eastern workers, possibly child labor (remember how happy they are when the witch is dead?)
Who knows? I don't think the author (Baum) actually ever said, but I guess if you look hard enough, you can find something in nothing.
But it's fun to think about,
Stinger