John Steinbeck was not the best or most brilliant writer America ever had. He may have a brighter legacy than any other, though, in part because he suggested wrath could be good. He inspired Cesar Chavez and John Kennedy; Bruce Springsteen and Woody Guthrie (and by extension Rage Against the Machine); John Ford and South Park. The Grapes of Wrath, published 75 years ago today, means just as much to the US now as it did in 1939, when the Dust Bowl destroyed the American west, the economy lay in tatters, a minority held the keys to the bank, and a vast migrant population wandered without homes or rights.

For those unfamiliar with the book (or at least for those who don't remember), The Grapes of Wrath tells a simple story: devastating weather and a bank's debt system force the Joad family off their farm; they go west, for work and good weather in California. They discover thousands of other migrants living in desperate poverty, exploited by the rich, abused by police, and abandoned by the government; they suffer, fight back and endure.



In the morning the dust hung like fog, and the sun was as red as ripe new blood. ... An even blanket covered the earth. It settled on the corn ... it piled up on the wires, settled on roofs, blanketed the weeds and trees.

Just a glance at The Grapes of Wrath reveals a familiar scene. The book opens with a nightmarish vision of drought and dust – the 1930s Dust Bowl that suffocated so many farms and families, forcing them to move or starve. Today, California faces record wildfires and what could be its worst drought in 100 years, the aquifers beneath heartland states are drying out, smog hovers over western cities and mining leaches water from shale states.



Facebook Twitter Pinterest A dust storm in Texas in 1935. Photograph: George E Marsh / AP

The book closes with biblical floods, washing away crops, homes and people; in 2014, the Gulf coast and east coast take years to recover from hurricanes – if not biblical in scope, then at least devastating in practice. Steinbeck never thought that humanity could goad the climate as we now know it does, but he still told a story of mankind's disrespect for the earth – and the penalties we pay for presuming invincibility.



Some of the owner men were kind because they hated what they had to do, and some … were angrey because they hated to be cruel, and some … were cold … And all of them were caught in something larger than themselves.

Steinbeck's wrath, however, isn't directed at the weather, but at those who abuse power. Banks chase farmers out with debt, and businessmen exploit migrant labor and disband unions. Steinbeck's America paired governance and capitalism while the majority labored for the sake the powerful's profit. (Steinbeck was unapologetic about certain socialist views, and the book's nominal hero, Tom Joad, says he's "bolshevisty".)



Today, megafarms and meat companies carve out sections of the market, divide and conquer farmers with debt, and control the food industry; the culprits include Cargill for corn, Tyson for meat, and Monsanto for its infamously creative genetics. (The film Food Inc and book The Meat Racket carefully document the rise and monopolistic methods of corporate agribusiness.)

Steinbeck's "monster" banks still evict families, still take bailouts, and still indenture Americans with debt. While families with fortunes survived 2008's "Great Recession", the unfortunate majority had to scrape by, losing homes and jobs, with millions still struggling six years later. Meanwhile, the fast food industry and Walmart stave off workers' unions as the strikebreakers of the 1930s did, only with corporate lawyers reciting appeals rather than guards swinging truncheons. When a venture capitalist suggests a "Kristallnacht" is coming against the "one percent", Steinbeck's observation that cruelty comes from fear and disappointment rings uncomfortably familiar.

"It's a free country." "Well, try to get some freedom to do. Fella says you're jus' as free as you got jack to pay for it."

Facebook Twitter Pinterest Police carry away a participant in a march organized by Occupy Wall Street in New York in 2011. Photograph: Tina Fineberg / AP

As if that weren't enough, the heroes of Grapes should be familiar: migrant workers mistreated and discriminated by the states. The Obama administration has deported more people (about 2m – nearly four times the documented population of Wyoming) than any other American government, and a congressional mandate to the Border Patrol requires they hold 34,000 undocumented migrants in custody every day. Authorities chase farmers without papers through forests and across deserts, splitting families and deporting lifelong residents. Nor do Steinbeck's stories of police abuse don't seem out of place in a country where local law enforcement sometimes merits federal inquiry.

To an extent, The Grapes of Wrath is simply a parable of disillusionment and survival set in the American west. It would appeal or annoy any generation, and it's got plenty of flaws – weak characters, flat style, blunt symbolism and melodrama, the list goes on. (The book opposes the classic "Wild West" libertarian ethos: instead it builds on the west's quiet history of socialism, like Woody Guthrie did, and feminism, as Georgia O'Keefe did.) But Steinbeck wanted to change minds and change society, and armed Grapes accordingly.



The Depression affected Steinbeck as war did Hemingway and exile did Nabokov: it changed his life and filled his work. Seventy-five years later, The Grapes of Wrath is a mirror to a country splintered by inequality, controlled by a minority, and facing climate "catastrophe". The world has come a long way since Steinbeck's day, but America at least still needs a voice as brutally honest as his. He debunked the myths of the American west (and the American dream) piece by piece, while also insisting that people were always better than the hardships they suffered. Steinbeck didn't want us to lose hope; he wanted us to get angry at those who would strip hope from us.



And what's wrath, after all? It's not the fury of a undoubting believer, nor the calculated, spittle-flecked performance of a pundit. Wrath sprouts when one person chooses greed over equality, and it grows anytime self-interest wins over compassion. Wrath ferments in disrespect and the abuse of power. Wrath is equal parts revenge and justice. Steinbeck's odd title – chosen by his wife from Civil War anthem The Battle Hymn of the Republic – is a call to outrage. In Steinbeck's world, wrath, when it protects the weak, can renew hope. Steinbeck didn't need to write clever, dense books, as his contemporaries did and as plenty of great writers do today. Steinbeck only had to remind America that its heart, from the heartland east and west, deserve respect, and that respect was worth fighting for – that wrath can be good.