How did America end up trapped in a nightmare of conspiracy theories, in which millions see the government as an evil 'deep state'? It didn't begin with Donald Trump, and it won't end with him.

In Ghosts of Iron Mountain, Phil Tinline traces the roots of today's fears back to the years after the Second World War, when America was the most powerful nation the world had ever known. He tells, in vivid, entertaining and brilliant detail, the story of a literary hoax that shocked a nation. Its impact - and its astonishing afterlife - reveal America's fears as you've never seen them before.

In 1967, at the height of the war in Vietnam, a group of New York writers cooked up a satirical response to the Dr Strangelove-like thinking prevalent in Washington. They concocted what appeared to be a top-secret government report into what would happen to the USA if permanent global peace broke out.

Report from Iron Mountain claimed that winding down America's vast war-making machinery would wreck the economy and tear society apart, necessitating draconian controls over the population. It was published as non-fiction - and was frighteningly convincing. Journalists tried to find out who had written it. Worried memos reached right up to the president. It became a bestselling cause celebre.

Even when the hoax was revealed, many refused to believe it wasn't real. Denial became proof of truth. The Report was seized on by eager figures on the far right and in the militia movement, who insisted that it revealed terrifying government conspiracies to pollute the environment, enslave Americans and even instigate eugenics. It helped to shape the movie that has done more than any other to revive conspiracy theory: Oliver Stone's JFK. And it spawned a second hoax, which has helped sustain its bizarre relevance right up to today.

Ghosts of Iron Mountain traces this story through a gallery of vivid characters, from the radical academic C. Wright Mills and the writers EL Doctorow, Victor Navasky and Leonard Lewin in 1960s New York, to the Hitler-loving far-right impresario Willis Carto, Oklahoma City bomber Timothy McVeigh, the conspiracy theorist William Cooper, L. Fletcher Prouty (the 'Mr X' of JFK), and the ranting broadcaster Alex Jones.

This is one of the great stories of our time, and an entertaining, compulsively readable narrative that reveals how nightmares about its own government drove America crazy.