In 1935, many families were forced to leave their farms and travel to other areas seeking work because of the drought (which at that time had already lasted four years).  Dust Bowl conditions fomented an exodus of the displaced from Texas , Oklahoma , and the surrounding Great Plains to adjacent regions. More than 500,000 Americans were left homeless. Over 350 houses had to be torn down after one storm alone.  The severe drought and dust storms had left many homeless, others had their mortgages foreclosed by banks, and others felt they had no choice but to abandon their farms in search of work.  Many Americans migrated west looking for work. Parents packed up " jalopies " with their families and a few personal belongings, and headed west in search of work.  Some residents of the Plains, especially in Kansas and Oklahoma, fell ill and died of dust pneumonia or malnutrition . 
The novel and movie do last, I think, because they are founded in real experience and feeling. My parents were scarred by the Depression, it was a remembered devastation I sensed in their very tones of voice, and "The Grapes of Wrath" shows half a nation with the economic rug pulled out from under it. The story, which seems to be about the resiliency and courage of "the people," is built on a foundation of fear: Fear of losing jobs, land, self-respect. To those who had felt that fear, who had gone hungry or been homeless, it would never become dated. And its sense of injustice, I believe, is still relevant. The banks and land agents of the 1930s have been replaced by financial pyramids so huge and so chummy with the government that Enron, for example, had to tractor itself off its own land.