The scarecrow represents American famrers. The scarecrow wants a brain and farmers were stereotyped as stupid. At the end of the book the scarecrow finds out he had a brain all along just like the farmers unit and solve their own problems.
The tin man represents a machine factory worker. The tin man keeps on getting his body parts replaced with tin after he keeps in chopping off his limbs and starts to become more "robotic" just like the workers in factories operated with machines.
The cowardly lion represents the politician the Nation Grange ran for president, Williams Jennings Brain. Williams Jennings Brain was a very good speaker but never backed up anything with actions. Therefore, he was thought to have no courage like the cowardly lion.
Wicked Witch of the East
The Wicked Witch of the east represented eastern factory owners.
The Wicked Witch of the West represents mother nature. For a long period of time, farmers in the south-west had to deal severe drought and dust storms. At the end when Dorothy pours water on her, it is symbolization for when the farmers overcome mother nature and the drought ends