They talked several times a day - John Foster as secretary of state and Allen as head of the CIA. But they didn't have to because they had a seamless understanding of each other's every thought - ''They knew, or believed they knew, the same deep truths about the world. Their intimacy rendered discussion and debate unnecessary.'' In the name of American exceptionalism, they opened secret jails (as the CIA did after 9/11), they recruited underground armies (now we call them contractors), and carried out or sponsored killings and bombings around the world (did someone say 'drone?'). Intriguingly, they came to their roles with a ready-made list of enemies. As former attorneys in the law firm of Sullivan & Cromwell, they first set about settling grudges with governments that had dissed their powerful corporate friends. In Guatemala, their client United Fruit Company was affected by land reform; and in Iran, a bank they represented was affected by the decision to nationalise the oil industry and within the first 18 months of their terms in office, they had disposed of President Arbenz of Guatemala and Prime Minister Mosaddegh of Iran, Kinzer said on NPR radio last week. But that was just a start. They fomented civil war in Indonesia; they bungled their way into the Vietnam War; went after Patrice Lumumbain The Congo and Fidel Castro in Cuba. During the Cold War they were affronted by nations being non-aligned, so they also wanted to go after Nasser in Egypt and Nehru in India.

''Neutralism was immoral,'' says Kinzer. ''It wasn't conceivable to [John Foster] that land reform in Guatemala could be a project that Guatemalans had designed to deal with a Guatemalan situation - he just assumed it had been ordered by the Kremlin.'' Presbyterian Calvinists, they saw the world in stark terms - there was only good and evil; those who were not Christian were heathens and savages. These two were duty-bound to go into the world to make sure their ''good'' triumphed, over communism and the rudeness of small governments that dared to stand in the way of US corporations. Kinzer cites three historic miscalculations, among many, by the brothers - a failure to understand the nature of Third World nationalism; their refusal to engage the Moscow leadership on the death of Stalin because to do so ''would help destroy the entire paradigm of the Cold War''; and they had no sense or worry about what today is called ''blowback''. Kinzer explains the Dulles modus operandi: ''John Foster Dulles would make speeches to the American people explaining that dangerous forces were at work in Country X … and while he was creating the public climate in which Americans would come to sense that Country X was an enemy, his brother would be actively working to bring down that government. ''Foster Dulles was then able to complete the circle by going on television and saying that the people of Country X have done just what we thought they might do - they've risen up and overthrown their tyrant.''

A powerful lobby served as protectors of the Dulles legacy, but these days not too many travelling Americans are aware of just who is being honoured at Washington's Dulles International Airport. The tribute was Eisenhower's. However, by the time the airport was to open JFK was in office and he wanted a name more suited to the 1960s - the lobby came alive and convinced the president of the error of his way. Kinzer's book will kickstart a new debate on the brothers' legacy. Historian Andrew Bacevich, a critic of the past decade of US foreign policy, has waded in: ''The Dulles brothers, one a self-righteous prude, the other a charming libertine, shared a common vision: A world ruled from Washington by people like themselves. ''They left behind a legacy of mischief.''