What was one of Steinbeck's primary purposes for writing The Grapes of Wrath?

John Steinbeck clarified his motivation in composing The Grapes of Wrath, when he kept in touch with Herbert Sturtz, in 1953: You say the internal sections were contradiction thus they were-that they were pace changers and they were that as well however the fundamental reason for existing was to hit the peruser unsportsmanlike