What is the theme in The Grapes of Wrath by John Steinbeck?

Industrialization and agribusiness make up the major theme of the story. Throughout the novel, the plight of the migrant farmers is repeatedly tied to the rise of industrialization, especially in the form of tractors. Big companies with mechanized ways of farming replace farmers who tilled the land by hand. The connection and pride the farmers once had has been severed. .