1973 saw enough turmoil in world affairs to easily justify Sir Alistair Horne’s subtitle to his book on Henry Kissinger, The Crucial Year. In January, Richard Nixon was inaugurated for his second term as president, after the second-largest electoral landslide in American history. Seven days later, the United States, North and South Vietnam, and the Viet Cong signed the Paris ceasefire agreement, and the U.S. suspended all military action against North Vietnam. It won Kissinger the Nobel Peace Prize.

February 1973 saw China and the U.S. establishing direct diplomatic relations after decades of mutual hostility. In April, Nixon accepted responsibility for bugging the Watergate building, while denying any personal involvement; the threat of impeachment loomed, and the scandal engulfed American politics for the rest of the year. May saw the Senate cutting off funding for the bombing of Laos and Cambodia, and the following month, in a striking moment for the policy of détente, Leonid Brezhnev somewhat prematurely announced that the Cold War was “over.”

Kissinger’s taste for back-channel diplomacy, his “extraordinary insecurity,” his short-fuse temper, his “slave-driving” of secretaries and underlings (who nonetheless seemed to have adored him), his strategic leaks to newspapers, and of course his view of diplomacy, are examined with a generally sympathetic eye.

In September 1973, General Pinochet staged his bloody coup d’etat in Chile, and the next month full-scare war broke out in the Middle East, when Egypt, Syria, Saudi Arabia, Iraq, and Jordan attacked Israel as the Jews were observing Yom Kippur. On December 23, the shah of Iran announced that the Gulf States would be more than doubling the price of oil from $5.10 to $11.65 a barrel, sending shockwaves through Western economies; London saw the most drastic fall in share prices since 1935. We think we are living in fairly interesting times today, but 1973 was a year to compare with 1848 or 1989.

At the very epicenter of each of these cataclysmic, world-changing events was Henry Kissinger, the national security adviser since 1969 and, from September 3, 1973, also U.S. secretary of State. This book intimately and expertly covers his multifarious activities during each of these great crises. Much of the overall architecture of the period will be familiar to readers, of course, but where Horne’s book differs from many others is that he adopts a frankly sympathetic attitude toward his subject. A highly distinguished British historian and the official biographer of Harold Macmillan, Horne states that “with Kissinger, as with Macmillan, unashamedly I came to like him, as a person, more over the years as work progressed.” If you are looking for yet another critique of Kissinger’s statesmanship, this is not the book for you.

“I deem myself free from that congenital anti-Americanism which besets some of my countrymen,” writes Horne, and that also goes for the anti-Kissinger assumptions made by most historians of the Nixon era, particularly in the academy. Kissinger himself is thanked in Horne’s preface for the “unstinting access” he accorded him, which gives this book another advantage over many of the hostile works. In many ways, it is the case for the defense, and none the worse for that.

With 33 tons of papers in the Library of Congress, Kissinger’s own three volumes of memoirs, the standard biography by Walter Isaacson (quoted almost to excess by Horne) and any number of secondary works and treatises, there is certainly no shortage of material on Kissinger, and Horne marshals it impressively to tell the story of how the various explosions of 1973, the year in which, in the author’s view, “the whole balance of power in Europe changed overnight.”

Over Watergate, Kissinger’s mission was, in his own words, “to attempt to insulate foreign policy as much as possible from the domestic catastrophe.” From having won more than 60% of all the votes cast the previous year, Nixon’s authority was utterly shattered by the late spring of 1973, making Kissinger’s task correspondingly difficult abroad. Using Kissinger’s (utterly exhausting) daily schedule to give immediacy to his narrative—we know everything right down to when Kissinger had his hair cut—Horne follows the decision-making process of the man he calls, correctly, “the most controversial of all Washington public servants.” Kissinger’s taste for back-channel diplomacy, his “extraordinary insecurity,” his short-fuse temper, his “slave-driving” of secretaries and underlings (who nonetheless seemed to have adored him), his strategic leaks to newspapers, his systematic bypassing of William Rogers, his predecessor as secretary of state, his unaccountability to Congress, and of course his general view of the value of diplomacy, are all examined with a generally sympathetic eye.

“Their goal was stability,” Kissinger wrote of Metternich and Castlereagh, the architects of post-Napoleonic Europe, “not perfection, and the balance of power is the classic expression of the lesson of history that no order is safe without physical safeguards against aggression.” That might just as easily have served as a leitmotif for Kissinger’s own diplomacy, especially détente, which served America very well until he left office in 1977, although it was no longer the right policy for the more self-assertive America of Ronald Reagan. Kissinger was the right man for his times, defending American interests in a dangerous period with minimal support from Congress. The splitting of the Communist world that he and Nixon achieved through the approach to China was in retrospect a signal act of far-sighted statesmanship.

Horne states that the Chinese and Russian initiatives “came from the ceaselessly restless brain of Richard Nixon, and not from Henry Kissinger.” Indeed they predated Kissinger’s arrival on the scene, having been thought up by Nixon when in opposition. “No more complex, tortured, and fascinating human being ever sat in the Oval Office,” Horne concludes about Nixon. Yet Kissinger was absolutely crucial to implementing Nixon’s foreign policy, and this book goes a long way towards explaining why.

What Kissinger’s brain was able to do—indeed, still is able to do 32 years after leaving public office—is to estimate the long-term implications of a policy in areas far removed from the immediate geographical or political impact of the policy itself. Like a gigantic Rubik’s Cube that is always turning, events reorient the international scene constantly, in ways that might not seem immediately apparent. Kissinger has always been able to compute these changes faster and more accurately than anyone else on the scene, which is why his advice is still sought after nearly a third of a century after he gave up the reins of power. How he did it in the year 1973 is explained by Horne in a masterly and compelling way.

Andrew Roberts’s new book, Masters and Commanders: How Four Titans Won the War in the West 1941-45 , is published by HarperCollins.