When John Steinbeck's classic novel The Grapes of Wrath  was published in 1939, it caused a sensation. It won the Pulitzer Prize and was the best-selling novel of the year. Just months later, in 1940, the book was turned into a film by John Ford, which was nominated for seven Academy Awards .
For readers today, Steinbeck's migration saga remains relevant as a piece of (dramatized) social analysis. It's essentially a road novel about the Joads, a poor Midwestern migrant farming family. Throughout the novel, the Joads fight to keep their family intact while fleeing the 1930s Oklahoma Dustbowl for the hope of farm work in California.
But once the Joads begin to migrate, the family begins to disintegrate.
The Joad grandparents aren't able to cope with life outside their native Oklahoma, and they both die early in the novel. A brother-in-law gets fed up with scraping by on itinerant farm work, so he leaves the family -- and his pregnant wife -- to seek other opportunities. The main character, oldest son Tom Joad, gets tangled in a labor dispute and is forced to abandon the family and live in hiding.
The disintegration of the Joad family illustrates that, although we are all subject to pressures and influences that bring us together and push us apart, migrants face unique and strong centrifugal forces that work against family unity.
Today, it's common to meet young men laboring on farms in the United States who haven't been home in years. They continue sending their family money saved from their $9-per-hour wages, but there is no human contact.
Even families that reconstitute themselves on the U.S. side of the border are not secure. The Urban Institute estimates  that 100,000 immigrant parents of U.S. citizen children have been deported to Mexico over the past 10 years.
Maria Santiago's family of farmworkers  is an example of how the immigration system can harm families. In 2010, Maria's husband went to Ohio to plant tomatoes. Normally she would accompany her husband north from their Florida home, but this time, because she was pregnant, Maria, 34, decided to stay behind.
Traveling by bus on his way back to Florida, Maria's husband was stopped by immigration officials and deported. Now he's in Mexico working to raise the money to return to the United States, but it's difficult for a laborer in Mexico without a formal education or marketable skills to obtain the money necessary to return.
Maria thinks about going back to Mexico. But for her U.S.-born children, Mexico is an unknown and unappealing destination. They are American.
In spite of Maria's story and thousands of similar stories, deportation probably impacts fewer families than the more gradual and less dramatic impact of an increasingly dangerous border.
Ernesto Alvarado, 40, has been doing farm work in the United States for 20 years, mostly in the American South. Although his parents live in the Mexican border state of Nuevo León, it has become too dangerous to cross back-and-forth with any frequency.
"If I go over there I can't come back," Alvarado said during a June 2011 interview in south Georgia. "I don't care about the money, but you can die on that trip."
Just as Steinbeck's poor Midwestern Scotch-Irish migrant farmers faced the Great Depression while struggling against Californians hostile to poor outsiders, today's immigrant  farmworkers also contend with fallout from the Great Recession compounded by escalated immigration enforcement and an increasingly violent border.
Andrew Wainer is immigration policy analyst at Bread for the World Institute  in Washington, D.C.