You should read
this one as well.
(Shame on me to post before I finish reading!)
In recent years, a number of scholars have pointed out inconsistencies between The Wizard of Oz and Populism.
In his 1991 book Populism: The Humane Preference in America, 1890-1900, Gene Clanton argued that Baum had indeed intended to write a political allegory. He agreed for the most part with Littlefield about the symbolism of each character with one important exception. To Clanton, the Wicked Witch of the West did not symbolize nature, but Populism itself. Clanton distinguished between right-wing and left-wing agrarian revolt and he pointed out that while Baum may have supported Bryan, he disliked the left-wing Populism that had such strong influence in the West. To Clanton, The Wizard of Oz was better suited to be an allegory of Progressivism rather than Populism.[15]
In Land of Desire, William Leach points to Baum's background in advertising and suggests that The Wizard of Oz does not offer any sort of Populist critique of capitalism. On the contrary, he argues, Baum wrote an upbeat story that affirmed the growing consumerism brought by industrial capitalism.[16]
Rather than a Populist critique of the excesses of capitalism, in this light The Wizard of Oz represents a pro-capitalist fable. Gretchen Ritter points out that it is possible to read The Wonderful Wizard of Oz as "poking fun at believers in the mysterious power of silver, criticizing the false value of green paper currency, and celebrating the power of gold when properly used by wise rulers."[17] She goes on to say that it's hard to refute the notion that Baum wrote a Populist allegory, given the prevalence of imagery the consistent with the Populist outlook. The alternate interpretations of The Wizard of Oz are certainly interesting but probably will not stop scholars from referring to The Wizard of Oz as a parable on Populism.