I always thought WASPs were young women called Missy who dressed in little pink cardigans and pearls and preppie young men called Lowell or Carter, fashion items really. Well, this gigantic volume, conceived on a scale of grandeur to rival the US Capitol itself, has put me right. Rooted in Puritan New England, the WASPs (White Anglo-Saxon Protestants) emerged in the 1860s as a would-be moneyed ruling class pitted against the brutish, vulgar, selfish tycoons who came into existence in the boom years after the Civil War. Driven by the ill-yoked ideals of Puritanism and Athenian democracy (as conceived by Thomas Jefferson), WASPs sought not just fuller lives but complete lives for themselves and everybody else. Their belief was that the 20th century would be the ‘American century’ and their aim was to make it so.

The top WASPs are the two presidents Theodore and Franklin Roosevelt, along with the latter’s wife, Eleanor. It’s entirely typical that Theodore and Franklin were distant cousins and that Eleanor was Theodore’s niece. All the WASPs are related to each other and you could go mad trying to work out how. They also have funny names either assigned at birth, such as Grafton Winthrop Minot or Trumbull Stickney, or acquired later as nicknames: ‘Fuzzy’ Sedgwick, ‘Babe’ Paley, ‘Fouf’ Payne Whitney. Other important WASPs have been judges, advisers to presidents, ambassadors, founders of museums or mysterious sages: Dean Acheson, Averell Harriman, Gertrude Whitney, Henry Adams. You won’t necessarily have heard of them.

Michael Knox Beran begins his exploration brutally by telling us that the WASPs are finished, quite dead. Edie Sedgwick, one of Andy Warhol’s muses, was the last desperate gasp of the WASPs, reduced to being brought to prominence (of a kind) by someone from Pittsburgh and then cruelly abandoned. She died of a drug overdose in 1971. Her father, Fuzzy, was bad enough, removing himself to California, where he turned his vast private estate into a version of the Playboy Mansion. The book goes backwards from there but things don’t get any better. Early on comes this extraordinary sentence: ‘There is … great difficulty in writing about people whose time has passed, who were bathed in the lukewarm bath of snobbery, who, with flashes of insight, were largely mediocre.’

Mediocre, but racked and strange. In the 1880s, John Jay Chapman, descendant of John Jay, the first chief justice of the United States, struck a friend in an argument about a woman. He went home and thrust his hand into the fire. He kept it there until it was burned away. This is the kind of Dante-esque journey through hell that all WASPs must undertake before emerging into the golden paradise of public service and a ‘complete’ life with poetry in it. Chapman entered politics. His stump was quite a draw. Soul turmoil and nervous complaints were compulsory for all WASPs. Beran diagnoses guilt induced by Puritanism as a contributing factor. But a lot of them never got beyond the hellish phase. It’s just an impression, but I would say many succumbed to alcoholism or insanity.

The WASPs were incredibly rich. Beran plays this down. Or perhaps it’s just taken for granted. Mostly the fortunes were acquired over generations. Although they claimed to despise the glitzy new money (Edith Wharton said of the Vanderbilts, ‘They are entrenched in a sort of thermopylae of bad taste’), they weren’t above marrying into it when necessary. John Pierpont Morgan was a rare WASP tycoon. He actually cared about democracy. But when it came to art, he mostly bought it by the yard. One day, he came across a receipt for a bust of Hercules he had acquired and asked his librarian where it was. ‘This bronze bust is in your library,’ she answered, ‘and faces you when sitting in your chair. It has been there about a year.’

Endicott Peabody, known as ‘Cotty’, is a big figure in the book. The founder, in the 1880s, of a tiny school in Massachusetts designed to nurture perfect WASPs, he was hardly the ordinary type of schoolmaster. He and his fellow founding teacher, William Amory Gardner, were millionaires. Gardner paid for the new chapel just like that. The school, Groton, was a WASP success story. Or was it? It’s still there, with, according to its website, an endowment of $475 million. Beran is a former pupil, but he keeps quiet about this. FDR went to Groton. Originally the school was to be like a monastery, with boys and masters living in monkish harmony, peering into each other’s souls in preparation for lives of civic duty. This didn’t quite work out. Visiting the school in 1902, Theodore Roosevelt urged the boys ‘not to take champagne or butlers with them on camping trips’. In later life, Cotty was tormented by the thought that really Groton was just a place for all these WASP men to form an old boys’ network.

The two champion WASPs were arguably the most popular and successful presidents ever. But Theodore’s famous mania, which drove him to overcome his childhood asthma through exercise, left him somehow trapped in boyhood, subject to wild but temporary enthusiasms. Cecil Spring Rice said, ‘You must always remember that the President is about six.’ FDR was exempt from WASP neuroses, which was not necessarily a good thing. Churchill said he was ‘a charming country gentleman’ with no habits of business. At Yalta, he treated Stalin as if he too had been at Groton. He smiled and waved and never answered a question if he could help it. Nobody knew whether he really understood the economics of the New Deal. His fellow WASPs thought he was a crypto-Bolshevik and booed as the presidential limousine left a WASP wedding. But he loved spying. His own wife’s FBI dossier was his favourite reading material.

Nobody will ever again memorialise the WASPs so vastly or with such erudition and dazzling cultural range. The book’s bold fragmentary structure and extended philosophical passages make it in places as challenging to read as The Waste Land itself – yes, T S Eliot was a WASP. It will perhaps become the definitive work of reference on the subject.

The WASP story is really the American story and the dilemmas that confronted the WASPs are intriguing: how to be a public person yet retain a viable inner life; how to be cultivated yet not remote; how to steer a path between virtue and power. It is classically American not just to have ideals but actually to believe they can be realised. In England, the WASPs would have retired to their country estates and built the odd parish hall. But in America you have to be worrying about America. It won’t leave you alone. The only WASP mentioned who seems to have had the right idea was Hugh Auchincloss. Gore Vidal, his stepson, wrote that after leaving Groton, Auchincloss found that ‘he was unable to do work of any kind. Since the American ruling class, then and now, likes to give the impression that it is always hard at work, or at least very busy, Hughie’s sloth was something of a breakthrough.’