The premier Cold War historian first met the premier Cold War diplomat in 1974. Then a very junior professor at Ohio University, John Lewis Gaddis asked the already iconic George Frost Kennan if he could interview the former policy planner and ambassador to the USSR for an article he was writing for Foreign Affairs. It was only a brief interview, says Gaddis, and they met “only a couple of other times” before Kennan agreed to let Gaddis become his authorized biographer in 1981. Finally released in November after 30 years of work, George F. Kennan: An American Life is a triumph of scholarship and narrative. It is the best book yet written on the most important American foreign-policy thinker-practitioner of the 20th century.

The book was widely anticipated. Not only was it three decades in the making, but Gaddis has emerged in recent years as one of America’s most prominent historians of world affairs. He teaches a popular course on grand strategy at Yale and writes frequently for the press. He received the National Humanities Medal in 2005 and was a confidant of President George W. Bush. And Gaddis long ago established himself as the foremost chronicler of Kennan: he not only wrote the definitive book on Kennan’s strategy of containment, he penned a series of provocative articles attempting to apply Kennan’s thinking to America’s post-9/11 strategic environment. Kennan was always horrified at misappropriations of his ideas by other policymakers and scholars—he did not foresee that his official biographer would be one of the culprits.

The relationship began on common philosophical ground. It might seem strange that Kennan, in 1981 one of the world’s most respected foreign-policy thinkers, permitted someone he barely knew to have exclusive access to his much sought-after personal diaries and files. But though he was not yet close to Kennan, Gaddis had already launched a mini-revolution in the scholarly understanding of the Cold War. Born in a small town in southern Texas in 1941, Gaddis earned his doctorate from the University of Texas and had his dissertation published in 1972 as The United States and the Origins of the Cold War, 1941-1947. Relying on just-released documents, the book transformed the traditional narrative of the Cold War and won several awards, becoming for more than two decades the standard source on the early years of the conflict. “It was an instant success in a way that any Ph.D. might dream about,” his friend Paul Kennedy, himself among the top historians working in the United States, later gushed.

Early scholars of the Cold War such as Herbert Feis and Arthur Schlesinger Jr. maintained that the conflict resulted from the Soviet Union’s intention to spread Communism across the globe and America’s corresponding determination to halt that effort. Later came revisionist historians—William A. Williams and Walter LaFeber senior among them—who argued that the Cold War was really the fault of the United States, which wanted to expand markets overseas.

The United States and the Origins of the Cold War was the definitive text of “post-revisionism,” which held that economic considerations were being overblown by the revisionists. Instead of the U.S. being pushed primarily by commercial motivations, Gaddis wrote, “many other factors—domestic politics, bureaucratic inertia, quirks of personality, perceptions, accurate or inaccurate, of Soviet intentions—also affected the actions of Washington officials.” The book struck a balance between the myth of American innocence that the first generation of historians had peddled and the equally unbalanced take of the revisionists. It was a middle ground that emphasized the narrow internal and external constraints early Cold War statesman operated within. It was also written and published at the height of the Vietnam War, when a nuanced perspective on American foreign policy seemed impossible to find.

In avoiding the poles of triumphalism and self-flagellation, by playing close attention to the evidence and empathizing with policymakers, Gaddis recalled the perspective of George Kennan. As a Foreign Service officer, head of State Department Policy Planning Staff, and as a National War College lecturer, Kennan had authored a series of speeches, articles, and State Department cables and telegrams from the mid-1940s to 1950 on the U.S.-Soviet relationship. The strategy he advocated came to be known as “containment,” which offered a middle way between making war on the Soviet Union and acquiescing in its expansionism. Instead of America launching an all-out effort to defeat the Russians, the U.S. should use “adroit and vigilant application of counter-force as a series of constantly shifting geographical and political points, corresponding to the shifts of maneuvers of Soviet policy,” Kennan wrote in his famous “X” article in Foreign Affairs. As Gaddis noted more than 50 years later, “What Kennan opened up … was a way out: a grand strategy that rejected both the appeasement and the isolationism that had led to World War II, on the one hand, and on the other the alternative of a third world war, the devastation from which, in a nuclear age, could be unimaginable.”

As well as prescribing a median between total war and appeasement, Kennan also wanted America to avoid the extremes of defeatism and overzealousness. He called for a strategy that was “long-term, patient but firm.” He was asking for a form of moderation, just as Gaddis found something of a moderate way between opposing historical perspectives.

Indeed, Gaddis showed an uncanny ability to channel Kennan’s thinking. He released Strategies of Containment in 1981, a book that attempted to explain American strategic thinking throughout the Cold War to that point. It argued for “the idea of containment as the central theme of postwar national security policy.” Gaddis took Kennan’s strategic vision and argued that every postwar administration from Roosevelt to Reagan, liberal and conservative, Democratic and Republican, had operated within its boundaries.

In Strategies of Containment, Gaddis elaborated and elucidated Kennan’s strategy as no other thinker had done. He examined Kennan’s various writings and talks from the early Cold War years and illuminated their cohesiveness, nuances, and assumptions. If Kennan’s thinking from that era seemed contradictory and opaque to many, that was only because it lacked as shrewd and careful an outside observer as Gaddis to explain its complexity. As with the Gilbert schema outlining the secrets of James Joyce’s Ulysses, what once seemed baffling became clear once its design was revealed.

Like Gaddis’s first book, Strategies of Containment became the standard source on its subject. Kennan appreciated the effort. “Right after the book came out, I got a hand-written note from George, saying something like, ‘You have understood my views better than anyone else ever has’,” Gaddis says. Coming from Kennan, who felt himself chronically misunderstood, it was no small compliment. After Gaddis received a few more notes offering praise, he asked to become Kennan’s official biographer. The deal was this: Gaddis would get unrestricted access to Kennan, his papers, and his many diaries. Kennan would also encourage his friends and family to speak with Gaddis. In return, the biography would not be published until Kennan died. At the time of the pact, Kennan was 78. In five or at most ten years, both author and subject assumed, the book would be released.

As it happened, George Kennan lived until March 2005, when he died at the age of 101. The unexpectedly lengthy period between the Gaddis-Kennan agreement and the release of the biography allowed for several developments. First, Gaddis was able to interview Kennan repeatedly and extensively, and to meet him for less formal visits about once a year. The correspondence about the biography fills three boxes in the Kennan papers housed at Princeton. Gaddis also became friendly with Kennan’s family—George F. Kennan: An American Life is dedicated to the subject’s wife, Annelise—and got to know the diplomat-historian as a living human being as well as a historical figure. These meetings add texture to the biography, as Kennan is able to revisit—and revisit once again—events, ideas, and individuals. Second, Kennan was able to personally hand over some of his materials to Gaddis, including the only copy of the diary kept from 1970 to 2002, and even a diary in which Kennan recorded his often haunting dreams. Such personal contacts enrich the biography, enabling Gaddis to understand Kennan in a novel manner. No other writer on Kennan has come close to plumbing the depths of his fragile, tortured psyche as Gaddis does. Finally, because he lived until 2005, Kennan was able to observe and discuss many recent events. Most importantly, he saw the end of the Cold War he had helped diagnose and was able to reflect on the success of the strategy he had developed.

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George Kennan was a very different man in his later years. He was different from his younger self not only in his physical decay—which manifested itself in the slowness and incapacities that mark all who reach advanced years—Kennan was also a very different thinker. Though always ambivalent about America, the younger Kennan had once spoken in admiring tones at Oxford in 1958 of “how much this period abroad has caused me to love my own people” and had written a poem in his diary that read, “Oh my countrymen, my countrymen, my hope and my despair! What virtues you conceal beneath your slouching self-deprecation: virtues inconceivable to the pompous continental.” That Kennan appreciated jazz, baseball, and the American landscape, even as he castigated many features of his native country.

No similar odes to America were written in the last 30 years of Kennan’s life. By the end, he advocated dismembering the United States through regional secession and described his country’s physical environment as “a wasteland, a garbage dump, a sewer.” He believed the Reagan administration, not its Soviet counterparts, to be responsible for the escalation of the Cold War in the early 1980s. He wrote of “elements” in American society who needed an inhuman enemy “as a foil for what they like to persuade themselves is their exceptional virtue.” When the Germans celebrated the fall of the Berlin Wall, Kennan lamented that they were only motivated by the “hopes of getting more jobs, making more money, and bathing in the fleshpots of the West … was this, over the long term, what we really wanted?”

Kennan had always been curmudgeonly, harshly critical of modern life and industrialization. But these views had once been outweighed by affection for American virtues and strengths. In his later years, there were only laments about the pornography, anti-intellectualism, and commercialism that characterize the contemporary West.

As far as the success of American strategy in the Cold War went, Kennan saw no cause for celebration.

Nobody—no country, no party, no person—‘won’ the Cold War. It was a long and costly political rivalry, fueled on both sides by unreal and exaggerated estimates of the intentions and strengths of the other party… . That the conflict should now be formally ended is a fit occasion for satisfaction but also for sober re-examination of the part we took in its origin and long continuation. It is not a fit occasion for pretending that the end of it was a great triumph for anyone, and particularly not one for which any American political party could properly claim principal credit.

If anything, “The extreme militarization of American discussion and policy, as promoted by hard-line circles over the ensuing 25 years, consistently strengthened comparable hard-liners in the Soviet Union.”

Kennan believed the United States had no influence whatsoever on the dissolution of its Russian adversary. He called the belief “childish,” writing that “no great country has that sort of influence on the internal developments of any other one.” But in the 1946 article for which he was most famous, Kennan had written, “It is entirely possible for the United States to influence by its actions the internal developments, both within Russia and throughout the international Communist movement.” The latter-day Kennan was melancholy about his country and its direction and had no faith in its ability to withstand future challenges, of either the domestic or the international variety.

John Lewis Gaddis, it is fair to say, evolved in precisely the opposite direction. Like much of Kennan’s work, Gaddis’s early writings were striking for their relative moderation, their willingness to concede American mistakes as well as successes. If they saw events from the American perspective—historians then only had access to U.S. documents—they were nonetheless critical of American policies and decisions and tried to understand events from the Soviet point of view. “Kremlin leaders, too, looked to the past in planning for the future, but their very different experiences led them to conclusions not always congruent with those of their American allies” in World War II, The United States and the Origins of the Cold War reads. “It seems likely that Washington policy-makers mistook Stalin’s determination to ensure Russian security through spheres of influence for a renewed effort to spread communism outside the borders of the Soviet Union.”

But then the Berlin Wall came down. With access for the first time to Soviet archives, Gaddis became convinced that his previous conclusions had been, in a way, too complex. The truth was simpler than a story of missed opportunities, tragic mistakes, and misperceptions. His first book to reckon with the flood of new documents was 1997’s We Now Know: Rethinking Cold War History. It contained a much starker view of Soviet objectives: “as long as Stalin was running the Soviet Union a cold war was unavoidable,” Gaddis wrote. “And given his personal propensity for cold wars—a tendency firmly rooted long before he had even heard of Harry Truman—once Stalin wound up at the top in Moscow and once it was clear his state would survive the war, then it looks equally clear that there was going to be a Cold War whatever the west did. Who then was responsible? The answer, I think, is authoritarianism in general, and Stalin in particular.”

Gaddis’s 2005 book, The Cold War: A New History, was even blunter. “Stalin’s goal, therefore, was not to restore a balance of power in Europe, but rather to dominate that continent as thoroughly as Hitler had sought to do.” Qualifications were fewer, conclusions surer, optimism stronger. The Cold War “began with a return of fear and ended in a triumph of hope.”

In a scathing review of The Cold War: A New History for the New York Review of the Books, the late historian Tony Judt called Gaddis what to Kennan would have been the greatest insult of all: an unapologetic American triumphalist. “John Lewis Gaddis has written a history of America’s cold war: as seen from America, as experienced in America, and told in a way most agreeable to many American readers,” Judt wrote. “Here and elsewhere, as the Communist regimes fall like bowling pins and the U.S. emerges resplendent, vindicated and victorious, The Cold War: A New History reads like the ventriloquized autobiography of an Olympic champion.”

Gaddis today waves Judt’s criticisms away. “I think it was just Tony Judt,” he says. “Every now and then he did that kind of review—a blowtorch review. I didn’t really take it seriously.” This seems unfair to Judt, who was arguably the preeminent historian of modern Europe of his generation.

Gaddis denies that his political thinking has shifted at all. In his view, what has changed is the evidence. Once the Cold War ended and non-American sources became available, “the biggest change for me was that I came to see that ideology was a lot more important on the other side than I had thought it was.” He continues: “I and a lot of other people had made the argument that even though the Soviets talked a lot about Marxism-Leninism and all of that, that it was window-dressing, it was rhetoric, that their minds really functioned very much in the same realist, balance-of-power tradition that Western statecraft functioned in. But as we got the documents, that turned out not to be true. It was true that they believed their own ideology—the same is true of the Chinese. That was an eye-opener… I and most of my historical colleagues have come around to that view, based on the Soviet and Chinese documentation.”

Not so. Melvyn Leffner is one of the few scholars able to go toe-to-toe—or archive-to-archive, as it were—with Gaddis in the field of Cold War history. A professor at the University of Virginia, he is the author of several prize-winning books on the Cold War and co-editor of the definitive Cambridge History of the Cold War.  He believes that Gaddis’s view is simplistic. “There are elements of truth in [Gaddis’s] view, but broadly speaking, the new documents have revealed that there was somewhat more importance of ideology on both sides.” According to Leffner, whatever was motivating the Soviets, they acted in a highly opportunistic and contingent fashion, without a master plan to dominate the globe. “They, like the Americans, were acting in both an offensive and a defensive manner.” Leffler does not see himself in stark opposition to Gaddis and has great respect for him, especially for his early work. “But I am positive a majority of historians assign much, much greater complexity to the origins of the Cold War than does John in his writings of the last 10-15 years,” he says.

It is not as if Gaddis’s perspectives on the Cold War have evolved in a vacuum. Like many of his countrymen, John Lewis Gaddis emerged from America’s victory in the Cold War emboldened about the possibilities of American power. When the 9/11 attacks occurred, he became a theorist who tried to provide cohesiveness to U.S. foreign policy. The attacks exposed “a level of vulnerability that Americans have not seen since they were living on the edge of a dangerous frontier 150 years ago,” Gaddis wrote. He praised the Bush administration for “immediately sens[ing] the significance of this new geopolitical situation.”

Though his compliment implies a sort of agnosticism, in fact Gaddis was a great supporter of George W. Bush’s foreign policy. His 2004 book Surprise, Security, and the American Experience was an implicit defense of that policy, which had come under sharp attack. According to Gaddis, Bush’s ideas about preemption, unilateralism, and expansionism were not a departure from American traditions, as many held. They in fact had far deeper roots than most Americans knew, and the administration was simply following in long line of U.S. statesmen in their attempts to remake the world, or at least a big chunk of it.

Leffler again emerges here in contrast to Gaddis. On the tenth anniversary of 9/11, Leffler wrote an essay in Foreign Affairs backing up the argument that the Bush administration’s foreign policy was not a departure from American traditions. But Leffler saw this as a negative thing, while for Gaddis it was liberating: “It seems to me on balance American imperial power in the 20th century has been a remarkable force for good, for democracy, for prosperity,” Gaddis said. He was on board with the most messianic beliefs of the era: “Where I would like to be 15 or 20 years from now is living in a world in which the international community as a whole justifies action, retaliatory or pre-emptive as the case may be, whenever brutal authoritarian regimes are practicing their terrible arts on their own people,” Gaddis wrote. “The world now must be made safe for democracy, and this is no longer just an idealistic issue; it’s an issue of our own safety.”

In fact, Gaddis remained enthusiastic even after the most hubristic period of the Bush administration—2002-2003—had passed. He offered President Bush numerous Oval Office seminars and helped write his second inaugural address in 2005. That speech was notable for its deep devotion to American foreign policy’s messianic traditions, the rhetoric so excessively idealistic that even Republican loyalists like Peggy Noonan and National Review’s Rich Lowry criticized it. In the fall of 2008, Gaddis wrote an essay in the American Interest suggesting that the long-term aim of American foreign policy should be the complete end of tyranny on earth. “A global commitment to remove remaining tyrants could complete a process Americans began 232 years ago,” he wrote. Again, these arguments are notable not just for their audacious scope and crusading spirit but for their timing. By autumn 2008, most American intellectuals were attempting to figure out how to retrench from commitments overseas, not opting for dramatic new challenges.

George Kennan and John Lewis Gaddis may have started their long collaboration at roughly similar points, but they moved in opposite directions as the years went by. Kennan was always a child of World War I, which he called “the greatest catastrophe of Western civilization.” Gaddis seems most influenced by the remarkable end of the Cold War, which left America standing unchallenged as the great power of the world. For Kennan, by the end, America could do little right. For Gaddis, America seems capable of little wrong. The book that brings them together, George F. Kennan: An American Life, probes to an unprecedented degree the erratic brilliance of the great diplomat. But it is difficult to avoid the conclusion that both Kennan and Gaddis devolved as foreign-policy thinkers as time went by.

Jordan Michael Smith, a contributing writer at Salon, has written for the New York Times, Washington Post, and Boston Globe.