Well, in 'The Grapes of Wrath, An American Novel', a major theme is the journey. The Joad family's long and arduous journey from Oklahoma to California represents not just a physical movement but also a spiritual and emotional one. Additionally, the theme of community is there. As the migrants come together, they form a sort of community that helps them endure. And of course, the theme of the land and its significance. The loss of their land in Oklahoma is a huge blow to the characters, and the hope for new land in California drives them.
One of the main themes is the hardship of the Great Depression. The Joad family, for example, faces poverty and displacement. Another theme is the power of family. Despite all the difficulties, the Joads stick together. Also, social injustice is a big theme, as the migrant workers are exploited by the big landowners.