During the Great Depression, a drought struck the Great Plains region of the United States, further worsening already bad economic conditions that resulted in part from the stock market crash of 1929. Many farmers in the Oklahoma Panhandle and surrounding areas lost their farms and had to migrate to other areas in search of work. Many went to California, where their dreams of wealth and land did not usually pan out. These people, often referred to as "Okies," were the desperate people whose plight Steinbeck wrote about in Of Mice and Men and The Grapes of Wrath. Steinbeck knew their plight firsthand, as he had interviewed and traveled with migrant workers in California as a journalist in the 1930s.

Steinbeck's novelistic portrayal of the migrant workers is sympathetic. He shows how hard they work, and how little they earn as a result. For example, Lennie and George, the protagonists in Of Mice and Men, along with the farm hands, dream of settling down on their own land, but that dream is unlikely, as they can't earn enough to make their dream a reality. Instead, they travel from farm to farm and are often treated poorly by farm owners. In The Grapes of Wrath, the Joad family is displaced from their farm in Oklahoma and travels to California in search of a better life that doesn't materialize. They also become itinerants, traveling from farm to farm and not finding work. When the characters in the novel protest against their poor working conditions, they are often persecuted. Steinbeck writes empathically about the rootless existence of a people who were used to owning their own farms and having a settled and secure life.