One simple way to chart Britain’s decline and the rise of the United States over the last century is through the art of political biography. Crudely, the Americans produce the big books, continuously and at length. In Britain, the tradition of the multi-volume portrait of the mighty ended, more or less, with the Victorians.

There are exceptions. Charles Moore’s stately ascent of Mount Thatcher will see a second volume published next week, with a third threatened. Churchill continues to inspire admirers and detractors. Who else? A second-rank power gets the leaders it deserves, and most of ours do not deserve the truly big biographies.

In America, the belief persists that American politicians matter to the world. Edmund Morris has something to say about Teddy Roosevelt? Three volumes and one thousand pages should do. Robert Caro has thoughts on Lyndon Johnson? By volume four, the author had only just managed to get his subject into the Oval Office. Book five is on the way.

In American publishing and academia, none of this is regarded as excessive. The fact that Niall Ferguson intends to produce just two volumes on the life of Henry Kissinger – the first, sub-titled The Idealist, is published on Tuesday – will probably be regarded as a miracle of self-restraint. Given the author, that’s probably a fair assessment. The reality is that the first volume alone tops 1,000 pages.

The fact makes a point: size matters; length denotes importance. In American political biographies scale is intended as a measure of the men – generally men – commemorated. Was Kissinger, the eternal factotum, truly so important? Think counterfactually, as Professor Ferguson might say, and wonder what the world would have been like without this secretary of state and national security adviser. There might have been far fewer corpses in south-east Asia and Chile. What else?

Kissinger: 1923-1968: The Idealist is advertised at 1,008 pages. That, and Professor Ferguson’s self-advertised “contrarian” conservatism, should let us know where the historian stands. The page count says that Dr Kissinger is important, that Dr Kissinger matters. Now 92, and still with a keen eye on posterity, the figure whom the late Christopher Hitchens wanted to arraign for war crimes (and a few other things) seems also to have an appetite for rehabilitation.

Professor Ferguson, the Glaswegian at Harvard who claims to have turned his back on “intellectually shallow” Britain, is liable to sympathise. He certainly does not qualify as a natural enemy of all things “Kissengerian”. With his attempts to rewrite the history of the First World War and imperialism, his detestation of Barack Obama and his cheerleading for the Iraq war, the professor knows that ownership of the past is the first step to claiming the political future. That insight is also Kissengerian.

One historical fact, nevertheless, is that the perpetually “influential” Kissinger, routinely described as the statesman who has advised every president since Kennedy – though not Mr Obama – was in government for just a few years. From late in 1968 until the end of 1976, during the presidencies of Richard Nixon and Gerald Ford, he worked for those who held more power than anyone else on the planet. In that brief period a reputation was born.

So what would you say in his favour? Probably that the scholar who once spent time pondering the number of nuclear strikes that might be feasible in a crisis later helped to craft detente with the Soviet Union. “Strategic arms limitation”, little enough as it was, would stand in the ledger alongside Dr Kissinger’s work in “opening up” China to contact with the United States. The unlikely spectacle of Mr Nixon in Mao’s Beijing was largely the Secretary of State’s doing.

And on the debit side? Vietnam above all. Dr Kissinger helped to turn Nixonian “peace with honour” into a long, bloody debacle that ended in wholesale defeat for the United States and its South Vietnamese proxy. The consequences, as a matter of actions and reactions, are still being felt to this day. Disastrously, George W Bush and his helpers invaded Iraq in 2003 in large part to show that the US was “over” Vietnam. Mr Obama hesitates over committing troops overseas because the pattern remains: Vietnam, Afghanistan, Iraq.

Dr Kissinger’s famous realpolitik, though apparently treated to a dose of Professor Ferguson’s revisionism in the new book, has been the template for American foreign policy for close to half a century. When a crisis erupts, his advice is sought or, just as often, delivered regardless. The record shows, however, that the prospects for peace for America and the world have tended to improve whenever the Kissingerian solution has been ignored.

He was at the heart of the secret and criminal bombing of Cambodia, a campaign that created the conditions for a hellish civil war and, in short order, for genocide. He was callous and dismissive when US support for Pakistan in the Bangladesh war of independence led to similar horrors. He interfered, sometimes without the knowledge of his president, in wars, coups and the establishment of dictatorships the world over.

Chile and Argentina remain conspicuous, inglorious examples of the doctor’s diplomacy. In both cases, the Kissingerian style was to embrace brutal juntas rather than tolerate the mess called democracy. What Dr Kissinger termed realism and the US national interest – with the second taking precedence over the first, if push came to shove – were his lodestones. The damage caused to the standing of America in the world was immense. Those scars remain.

Nevertheless, and at severe risk to satire, Dr Kissinger wound up with a Nobel Peace Prize for his role in “ending” the Vietnam war. He was awarded the honour even while the conflict continued, a fact that stands as a metaphor, of sorts. The esteem in which the doctor has been held down the decades is utterly at variance with what is contained in the historical record. The good he did was outweighed, time and again, by the vast damage he helped to inflict.

Dr Kissinger deserves a big book or two. For a great many years he has personified the view that with a superpower’s responsibilities come inalienable rights. Even today, even with Mr Obama running down the clock, that Kissingerian belief in the uses of American power sits at the heart of the country’s foreign policy and its public debates.

You can hear echoes in the stump speeches of the candidates jostling for the chance to win the White House next year. The politicians running for the highest office in the greatest military power on earth obsess about defence spending, the restoration of American “greatness”, the unending contest with the unending succession of external threats. One after the other, they talk as though Vietnam can yet be won, as though amends can yet be made.

Dr Kissinger tells these people what they want to hear, just as he told their predecessors. That, not a brief spell in office, has been the source of his influence down the years. Despite all the failures, he presents himself as the subtle diplomat who offers them a way to victory. He has prospered by feeding a delusion. His trial is long overdue.