The book The Wizard of Oz by L. Frank Baum is considered by many to be an allegory dealing with William Jennings Bryan and the Populist movement of the late 19th century. Many of the novel's characters are considered to be representative of the following contemporary persons, archetypes, and ideas:
The Tin Man: the Northern industrial workingman
The Scarecrow: the Southern/Midwestern farmer
The Lion: William Jennings Bryan, believed by Baum to be a man who could unite the economic and cultural differences of North and South into a more cohesive United States if he would simply learn courage and try.
The Wizard: The president of the United States of America, whom the characters believe to be an all powerful man. In the end we find that he is nothing of the sort.
I have also heard the conjectures that:
The flying monkeys represent the Native Americans in their primitive nature.
The yellow-brick road is important combined with thesilver slippers (turned ruby in the film). The road symbolizes gold, the slippers silver, and the union of which refers to one of the more important aspects of the Populist political movement, more specifically the use of gold and silver to back up the American dollar.