Henry Kissinger doesn’t believe in retirement. At 91, having had a heart-valve operation three months ago, he is nonetheless publishing a book entitled World Order. As I happened to be interviewing him about it on 11 September, I asked him about his memories of 13 years ago. ‘I was in Frankfurt addressing a business group,’ he recalled in that voice of his that sounds like gravel has found its way into your car’s exhaust pipe. ‘A member of the audience had just asked a question when someone came on to the stage to say that he had an important announcement to make. I said that that may be, but I wanted to answer the question first, which I did, before the man said that New York had been attacked. It was about 2 p.m. German time and I needed to go next to Beijing, but my plane was grounded. For the first few hours there were theories that the attacks had been undertaken by South American drugs cartels or other organisations, but the suicidal nature of them led me immediately to assume that this had emanated from the Middle East.’

Fast, decisive and ultimately accurate perceptions are Kissinger’s forte, and the reason his global clients still pay Kissinger Associates millions of dollars a year for his counsel. Yet his offices on Park Avenue and 51st Street in Manhattan are more functional than plush; for work rather than schmoozing.

The previous night I had seen the searing new documentary The Fall of Saigon in an Upper West Side cinema, and so I asked him how those chaotic days in April 1975 had affected his worldview. ‘I think a very great deal about the trauma of Saigon,’ he said. ‘It’s something that must not happen again. America has fought five wars since 1945 and has gained its objectives in only one of them, the Gulf War. The tragedy of America is that it entered all the wars with a consensus in favour of them, but within a defined period the legitimacy of the war became a major domestic issue, with some people arguing that withdrawal was the only legitimate objective.’

‘Had it not been for Watergate,’ he continued, with emotion in his voice nearly 40 years after the events he’s describing, ‘the North Vietnamese invasion would surely have been opposed. If there was a major breach of the peace agreement [that he signed in Paris with the North Vietnamese foreign minister Le Duc Tho], we would have used American air and sea power to prevent a victory, which is what was needed. There had been no American ground forces in the South’s defeat of Hanoi’s 1972 offensive, after all. But for Watergate we would have defended the peace agreement by the same means. It was the great American tragedy that Watergate prevented us.’

Although his book is certainly not about Barack Obama — its high points come with Richelieu’s Realpolitik, Metternich’s Legitimist and Bismarck’s ‘Blood and Iron’ power-politics — it was fair to ask whether the current president was adding or detracting from the hope of restoring order to today’s world. So I asked whether leadership was important, considering that the US had no distinguished presidents in the three-and-a-half decades between Lincoln and Teddy Roosevelt when it rose to world prominence. ‘Leadership is absolutely vital if there are comparable countries which can affect the security of the world you live in,’ Kissinger replied. ‘Between Lincoln and Roosevelt’s time, America was protected by huge oceans and, in practice, by the British navy. Today, it’s different, and the obsession of the Obama administration has been for retrenchment.’

Kissinger is clearly nostalgic for more direct US action in defence of its interests. ‘In 1904 a resident of New Jersey called Ion Perdicaris was kidnapped by Moroccan brigands led by someone called Mulai Raisuli,’ he tells me. ‘The State Department sent a message demanding “This government wants Perdicaris alive or Raisuli dead.”’

World Order is a paean to the system of sovereign-state interactions named after the Peace of Westphalia, which ended the Thirty Years War. It didn’t take place in one of the palatial summit meetings that Kissinger is used to — as he points out, the Swiss envoy ‘lodged above a wool weaver’s shop in a room that stank of sausages and fish oil’ while there were only 18 beds for the 29 members of the Bavarian delegation. Nevertheless it was an enduring success, for as Kissinger told me, ‘If one considers world order as in part defined by the prevention of war, then the Westphalian system is uniquely western. In every other region of the world, peace has been achieved by various forms of empire, such as by the Chinese and Islamic. The Westphalian system, however, has characterised relations of western nations since 1648, and was then spread around the world by the imperial powers. When people talk about the violation of international law and appeal to the Westphalian system, that is not accepted in many parts of the non-European world.’

Yet the nationalism unleashed by the Westphalian system hardly discouraged war on the European continent. Kissinger ascribes the tragedy of 1914 to myopic leaders who had no idea of what they’d unleashed, adding: ‘I think that if Teddy Roosevelt had been president during the war, he might have attempted a negotiated outcome along the lines of his successful peace negotiations between Russia and Japan in 1905, and it would have been better to end the war without domestic upheaval and turmoil across Europe.’ I asked what he’d have done had he been Woodrow Wilson at the Versailles Peace Conference. ‘I would have tried to build on the Treaty of Vienna and make an effort to bring Germany into the international system.’ As he puts it in the book: ‘Germany has for much of history been either too weak or too strong for the peace of Europe.’

I asked about the place Protestantism played in the creation of the Westphalian system. ‘Protestantism has been a major engine of invention, a driving force in the Age of Discovery and it created the notion of national sovereignty and the doctrine of the state,’ Kissinger told me. ‘It couldn’t have happened without Protestantism. Yet I wonder what might have happened if a tolerant Holy Roman Empire had adopted Cardinal Richelieu’s policy in which Europe evolved a much more inclusive system? If religious orthodoxy hadn’t been imposed by Charles V and his successors, a more peaceful Europe could have emerged upon Richelieu principles.’ Along with Konrad Adenauer, Cardinal Richelieu, who directed French foreign policy from 1616 to 1642, is a hero of this book. ‘I regard Richelieu, Metternich and Bismarck as the pre-eminent Continental statesmen who analysed correctly the power relations — including ideological relations — of their world, and who were moreover willing to act upon them. Britain also had a number of outstanding statesmen in its own right — Palmerston, Disraeli, Gladstone, Salisbury — whose primary focus was the global equilibrium.’

Kissinger clearly worries that with the 24/7 news cycle, statesmen have less time for reflection than they used to. ‘Richard Nixon didn’t like to concentrate too much on the minor details of problems,’ he said, ‘so he spent a lot of time in semi-secret alone, working things out with his yellow pad. He had a lot of time to reflect and discuss in those days. Of course that didn’t mean we always got everything right. In 1969 I said that we wanted to expel the Soviet Union from the Middle East. It was true, but it was a mistake to say so. When I arrived in Washington, I didn’t know anything about news cycles. Nixon knew about them as a politician but he had his own work habits. We certainly didn’t have people coming in giving us news updates all through the day.’

In part he blames the dominance of the internet, saying, ‘One needs to differentiate between information, knowledge and wisdom. In the internet era they tend to get mixed up. The more time one spends simply absorbing information, the less time one has to apply wisdom. And then there’s common sense. Lord Salisbury had long periods of reflection in which he applied wisdom and common sense.’

Since this is the man who along with Nixon brought China into the international system on their visit to Chairman Mao in 1973, it was natural to ask whether the Chinese would be net contributors or detractors from the world order of the future. ‘They are not natural imperialists, so they will be torn if they become the strongest power in the world. There will be some Chinese who will insist that the prevailing world order must reflect this new reality, but they are not driven by their culture to impose this. But they do want to be respected. I don’t believe the Chinese state is moving towards a magic date at which they will start building an empire. In the South China Sea, for example, for the Chinese it’s not a question of strict dominance as such, because they know that if they try to close the sea lanes there would be a clash, but it is instead a matter of asserting their nationalism at a time when they’re going through enormous domestic change. A senior Chinese figure told a group of us recently that the South China Sea question should be decided by a future generation.’

If there should be future hostilities between any of the great powers, Kissinger believes it will probably at least start in cyberspace. ‘If our banking system were to be shut down by an adversary there is no equivalent step to retaliate, since the other side’s banking system would be less global than ours. It would have to be a different step. I think war could start in cyberspace and escalate in ways none of the leaders could predict, along the 1914 model.’ Yet has the United States the willpower to fight a cyber war? In his book he describes America as ‘an ambivalent superpower’, so I asked him when this ambivalence began. ‘Vietnam,’ he replied. ‘That was when the moral basis for American foreign policy was challenged for the first time in our history.’

Yet today, he considers, the situation is worse than during Vietnam. ‘I don’t see the wisdom in modern politicians that I once saw in men like Dean Acheson, David Bruce, or George Marshall. In my day the northeastern establishment dominated foreign policy formulation, but the composition and distribution of our population is very different today. There are fewer shared global concepts and experiences among the groups making high policy.’ There’s also isolationism; is he worried by the libertarian Kentucky senator Rand Paul, who is likely to run for the Republican presidential nomination in 2016? ‘Paul is an intelligent man, who might learn on the job. But it is not a risk we should take.’

Talk of the great panjandrums of the policy-making elite allow Kissinger to reminisce about the time he briefly met President Truman in 1961, when he was a consultant for President Kennedy. ‘I said that we’d already learnt in the administration that the fourth arm of government was the bureaucracy, which could constrain the powers of everyone, even the President. Truman told me that this was bullshit; the President can substantially do what he wants, provided he knows what that is!’ If President Obama needs to remind himself what he wants in foreign policy, all he needs to do is read World Order.