Just before Vidal arrived, the poverty-wreathed Guatemalan people had elected a left-wing president called Jacobo Árbenz Guzmán. They wanted him to introduce a minimum wage and start taxing the US mega-corporation, the United Fruit Company, that dominated the country's only industry, banana-growing. The outraged United Fruit Company acted to preserve its profits – by getting Washington to topple Árbenz and install a dictator. The phrase "banana republic" entered the language. (Bananistan for a central Asian variation.)

"I was astonished," Vidal says. "I had known vaguely about our numerous past interventions in Central America. But that was the past." He discovered that Senator Henry Cabot Lodge was leading the charge, and "I didn't believe it. Lodge was a family friend; as a boy I had discussed poetry with him". He says he realised then he had been fighting "for an Empire, not a republic". His grandfather, he resolved, had been right all along: wars only serve elites.

He rapidly became the leading left-wing critic of American foreign policy. He warned against every war from Vietnam to Iraq, often with extraordinary prescience. At the height of George W Bush's post-9/11 popularity, he said: "Mark my words – he will leave office the most unpopular President in history."