What are the motifs in The Grapes of Wrath by John Steinbeck?

Traditional leadership roles changing is a motif through the novel. Once the land is taken from the sharecroppers, the women take control of the family unit rather than the man. We see this clearly with Ma Joad. Big Business takes on a menacing leadership role in the families of these migrant workers by subjugating them. Unions also grow in leadership roles as men are forced to fight back against corporate abuse.