Why would L. Frank Baum write an entire story like the Wizard of Oz, just to explain what Populism was like?

During the decades between world war i and world war ii, american foreign policy was characterized by a) large-scale military mobilization in anticipation of the second world war. b) aggressive imperialism as the united states gained control of much of the pacific. c) increasing federal control of the american economy to battle the effects of the great depression. eliminate d) increased isolationism as the united states focused on domestic issues instead of involvement in international affairs.