Hinge Points
An Inside Look at North Korea's Nuclear Program
Siegfried S. Hecker, with Elliot A. Serbin




Mount Mantap was never the tallest peak in North Korea’s rugged Hamgyong range. As day broke on September 3, 2017, it was about to become even shorter. Throughout the morning, North Korean scientists and technicians busied themselves at the base of one of Mantap’s slopes preparing for what they hoped would be a watershed moment in the development of their country’s nuclear program. During the last weeks of August, they had readied diagnostic instrumentation, fortified construction efforts, and assembled and emplaced a nuclear device within the tunnels that burrowed deep into the mountain, which had already been shaken by five previous nuclear tests.1 Now, they reviewed instruments and equipment housed in sheds outside the north portal, and trudged through a muddy courtyard to the command center, where they waited anxiously for the results of their years of effort. At 12:36 pm, the mountain shook. Within a fraction of a second, a powerful nuclear reaction took place, blossoming violently with devastating heat and pressure. It annihilated the test device, blasting a large spherical cavity within the mountain, and—unexpectedly—dropping Mantap’s 2,205-meter peak by half a meter and bulging it out sideways about 3.5 meters.

The ensuing 6.3 magnitude earthquake set off by the explosion reverberated throughout North Korea, into neighboring China and South Korea, and around the world. It triggered the sensors of the U.S. Geological Survey and the Comprehensive Nuclear Test Ban Treaty Organization, which monitor the globe for seismic activity.2 Just hours before the blast, the Korean Central News Agency (KCNA) had released photos showing North Korea’s leader, Kim Jong Un, inspecting a nuclear device. In one remarkable photo, Kim appears not giving orders but almost as the student, attentively following the instructive gesture of Dr. Ri Hong Sop, identified as director of the Nuclear Weapons Institute. Following the test, the Nuclear Weapons Institute called the test device a two-stage thermonuclear bomb—that is, a hydrogen bomb—small enough to fit inside the nose cone of the North’s long-range missiles, photos of which had been conspicuously displayed on the wall behind Kim.3

It remains impossible to determine whether the North had tested the device shown in the photos, but the explosion yield estimated from seismic data was 200 to 250 kilotons,4 about fifteen times the size of the August 1945 Hiroshima explosion and consistent with a yield from a hydrogen bomb. The last time a device of such power was detonated anywhere in the world was in a May 1992 nuclear test in China. The United States and the Soviet Union had not exceeded a blast of 150 kilotons since they signed the Threshold Test Ban Treaty in 1974. Regardless of the exact design of the North’s test device, there was no doubt that North Korea had demonstrated a new capability to inflict damage on a massive scale.

Following the nuclear test, on November 28, North Korea launched an unarmed ballistic missile almost 4,500 kilometers into space before its pieces fell back to Earth in the Sea of Japan. The U.S. government and independent analysts quickly assessed that the missile, dubbed Hwasong-15 by the North, had intercontinental range, meaning that it could put the entire United States within reach.5 North Korean state media released photos of Kim, illuminated against a towering, camouflaged transporter-erector-launcher (TEL), inspecting the missile before launch as well as Kim watching images of the missile’s flight path from an observation station. The Hwasong-15 test was the latest in a robust development schedule that the North had followed throughout 2017, during which it tested several ballistic missiles with newfound intermediate and intercontinental range.

All told, these two major events—the North’s test of a likely hydrogen bomb in September and a new intercontinental ballistic missile (ICBM) in November—underscored what had been a dangerous and unsettling year on the Korean Peninsula. The significant advancement of North Korea’s nuclear arsenal exacerbated the existing military threat that the North’s conventional, chemical, and nuclear forces posed to the United States and its allies in Northeast Asia. While North Korea would need more testing to improve the safety, reliability, and performance of its nuclear-tipped ICBMs, events in 2017 served notice that it was well on its way. The North had already demonstrated that it almost surely could reach South Korea or Japan with nuclear-tipped missiles, and now there was, for the first time, a possibility that it could reach the U.S. mainland as well. In less than six years after assuming the reins of the Kim dynasty in North Korea, the young Mr. Kim had fulfilled the dreams of his father Kim Jong Il, and grandfather Kim Il Sung, to possess a sufficiently menacing nuclear arsenal to deter the United States.

What made 2017 especially dangerous was that these rapid-fire technical developments took place as the political relationship between Washington and Pyongyang had become increasingly tense. The provocative rhetoric and threats of military force by both Kim Jong Un and U.S. President Donald Trump—backed by their respective nuclear arsenals—posed a great risk to international security. As Trump’s advisors debated whether the United States should initiate a “bloody nose” strike—a limited, preventive U.S. attack on North Korea’s nuclear assets and/or its short- and long-range delivery systems—Trump threatened that North Korea’s continued missile and nuclear development would be “met with fire and fury like the world has never seen.” And he stood before the UN General Assembly in September 2017 to warn “Rocket Man” that, if forced to defend the U.S. or its allies, he would “have no choice but to totally destroy North Korea.” Kim Jong Un responded in a statement with a ferocity that stunned even North Korean diplomats and caused many Americans to scramble for their dictionaries: “I will surely and definitely tame the mentally deranged U.S. dotard with fire.”

The fear of nuclear war in 2017 was heightened because so little was known at the time about the two leaders with their fingers on the nuclear button. Kim Jong Un, who had assumed power in North Korea in late 2011, was young and viewed in the United States as inexperienced and unpredictable. The U.S. news media often portrayed him as crazy or homicidal. Even less was known about the military leadership that commanded his strategic rocket forces. President Trump was equally inexperienced and, arguably, even more unpredictable. Compounding the problem was the lack of a regular, direct line of communication between Washington and Pyongyang.

North Korea was able to build its present-day nuclear arsenal against all odds and often in plain sight despite being in the crosshairs of every U.S. administration for the past thirty years. Every American president has vowed either to not let North Korea obtain the bomb or, once that ship sailed, to achieve its full disarmament. The North’s nuclear program was restrained but not eliminated during the Clinton administration; challenged, demonstrated, and then unleashed during the George W. Bush administration; greatly expanded during the Obama years; and became a menacing threat during Trump’s first year when Washington and Pyongyang nearly stumbled into a nuclear confrontation in 2017. A year of rapprochement in 2018 was followed by Kim Jong Un pulling back from diplomacy. The North has continued to cement its status more convincingly than ever as a state with a nuclear arsenal. This is the stark reality that leaders of the past three administrations must live with and that the current administration faces. It cannot be explained away or left on the foreign policy back burner indefinitely.


As I got more deeply involved in the Korean nuclear issue, it became increasingly clear to me that there was a dismayingly misleading narrative in the United States about how North Korea progressed from zero nuclear weapons in 2001 to an arsenal of close to fifty weapons some twenty years later. The conventional wisdom I encountered again and again was that good faith American efforts to halt the North’s nuclear program were circumvented by the North’s repeated violations of diplomatic agreements. Over the years, I found this perspective to be neither true nor helpful. It lets Washington off the hook too easily for its own failures and does not tell us why we are in the current predicament. Rather than cling to an unflinching belief in North Korea’s perfidy and to a narrative that the Kims trapped Washington in manipulative cycles of “provocation, extortion, and reward,” this book takes a fresh look at North Korea’s technical and political developments and how they are intricately intertwined.

Technical advances or setbacks in the North’s nuclear program opened or closed diplomatic options, just as diplomatic advances sometimes were a brake on technical progress. Failures in the laboratories or on the testing grounds may have required turning to diplomacy to buy time to correct problems. At other junctures, diplomatic progress gave Pyongyang new reasons to consider throttling back technical advances. At the same time, active diplomacy and agreements sometimes constrained technical options by limiting specific steps (such as tests) or allowing on-site presence of inspectors. In the subsequent chapters, I detail how these technical and diplomatic developments proceeded over two decades.

Moreover, the close and parallel examination of technical and political developments is crucial because perceptions of technical capabilities can be as important as reality. In other words, one must differentiate what Pyongyang wants Washington to believe from the reality on the ground. Over the years, Pyongyang has publicly hyped its nuclear and missile advances more often than it has tried to hide them. Separating perceptions from reality requires a certain level of in-country presence. U.S. intelligence agencies had little, if any, assets in North Korea, which combined with the closed nature of the regime, made it a difficult intelligence collection target. The intelligence community was dramatically wrong in several of its key North Korea estimates, and even when correct, the information was often not packaged in a manner useful to negotiators and, just as often, was not used effectively or manipulated by the policymakers who worked with negotiators.

As the North Korean nuclear drama unfolded, I had the benefit of a front-row seat, beginning with my first visit in 2004. My assessment of the North’s nuclear journey was informed by the extraordinary access Pyongyang gave me to its nuclear facilities and its nuclear staff for seven consecutive years. I was there by invitation, not as an inspector. Rather than hiding its nuclear progress, Pyongyang sought a certain level of transparency, primarily to try to convince Washington that it had a credible nuclear deterrent. My access to its nuclear facilities and the level of discussion with the North’s technical experts went far beyond what they typically shared with inspectors or what they professed through government propaganda. There was little posturing because they understood that I knew my way around nuclear facilities and nuclear weapons.

I began my involvement with North Korea with pretty much a blank slate. Although while at Los Alamos I had traveled to most countries with nuclear programs, I had not visited the Korean Peninsula and had little understanding of Korean history and culture. As it turned out, I was fortunate. My early visits provided a crucial education on the political front, thanks to Stanford University Professor John W. Lewis, who assembled his Track 2 delegations with individuals who had intimate and longstanding experience on North Korea. Lewis was a respected Asia specialist who had been engaged in Track 2 dialogue with China in the 1970s and with North Korea beginning with his first trip in 1989. He recruited Charles L. (Jack) Pritchard, an experienced diplomat and Northeast Asia expert who had just left government service, to join us for the first three visits. Pritchard had firsthand experience negotiating with North Korea from serving on the National Security Council and then as the State Department’s chief North Korean negotiator. Robert L. (Bob) Carlin was another key member of Lewis’s team. He first tackled the North Korea conundrum in 1974 as a CIA analyst. Later, he was chief of the Northeast Asia Division in the State Department’s Bureau of Intelligence and Research (INR), where he took part in all phases of U.S.–North Korea negotiations from 1992 to 2000. Carlin served in the Korea Energy Development Organization (KEDO) created to supply North Korea with electricity-producing nuclear reactors as part of the Clinton administration’s 1994 Agreed Framework nuclear deal. Beginning in 2006, Carlin joined us for visits to North Korea. I found Lewis and his colleagues to be indispensable tutors on politics and diplomacy.6

I learned quickly that Lewis and his team were highly respected in Pyongyang and had access to key government officials. This work was Track 2 at its most effective: people on each side with intimate familiarity with the politics and diplomatic record but who were not bound by the strictures of formal government negotiations. They were able to probe diplomatic openings, uncover potential red lines, and transmit warning signals. On the American side, the Track 2 engagements also provided a measure of continuity, which was typically lost within the government during presidential transitions. This was important because the North Korean side maintained continuity. For example, some of the key North Korean officials present during negotiations for the Clinton era nuclear deal are still there for President Biden’s term some twenty-five years later.

For seven consecutive years, from 2004 to 2010, Pyongyang gave us access to high-level diplomats, nuclear experts, and nuclear facilities. We used those visits to gain critical insights into the North’s nuclear developments and surmise how Pyongyang tied these to its political strategy. Pyongyang used our visits to signal its capabilities and its political interests to Washington. It ended with a 2010 visit in which North Korea surprised us and the rest of the world by revealing a modern centrifuge facility, demonstrating that in addition to their plutonium path to the bomb, they also had a plan with uranium.

After 2010, our Stanford University team continued to follow the North’s nuclear developments, but now from afar. We were greatly aided by the emergence of readily available commercial satellite imagery. Our team of experienced analysts benefited from what we had learned during our visits to the nuclear complex.7 Pyongyang also chose to selectively reveal its nuclear and missile advances. When the North stepped up its missile launches, it would augment the findings of foreign governments with its own propaganda. It routinely publicized photos of missiles, launch videos, technical details, and flight trajectories—often shown as being viewed by Kim Jong Un. New military systems, such as missiles and TELs, were displayed at huge military parades. Kim Jong Il and Kim Jong Un were shown visiting key defense facilities, inspecting critical equipment required to support the nuclear program.

Nuclear tests created their own observables by making the ground shake and triggering seismic signals that were registered by instruments around the world. The magnitude of the seismic rumbles allowed us to estimate the power of the explosions, which, in turn, provided clues as to how rapidly North Korea was enhancing its nuclear firepower. To augment what could be assessed from such measurements, and to make sure outsiders would not underestimate its capabilities, Pyongyang took the extraordinary step of publicizing photos of Kim inspecting two of its modern bomb designs. To ensure they lost nothing in translation, state media displayed nuclear missiles and drawings in the background of the bomb mock-ups to send the message that the nuclear devices would fit onto its missiles.

Pyongyang had moved on from our visits to using other means to lift the curtain to its nuclear progress, including missile launches, seismic signals, photographs, and videos. Our team also used these indicators to continue to assess the North’s nuclear trajectory, side by side with tracking the political developments. I continued to have regular contact with the American negotiation teams in all U.S. administrations and compared notes with Chinese, Russian, and South Korean government officials, scholars, and practitioners. Consultations with the Chinese, in particular, underscored the folly of U.S. administrations looking to China to solve the North Korea problem.

Bob Carlin was able to continue to track the political state of play with visits to North Korea in an unofficial capacity through 2017. Fortunately, Carlin was a seasoned veteran of official negotiations with North Korea and an astute observer of how Pyongyang functions and how it manages the news. He had experience on the ground through his more than thirty visits to North Korea over the years. Carlin was also adept at deciphering North Korean announcements and statements. To know what’s important in Pyongyang’s pronouncements, one must understand who said what and whether it is just propaganda or smokescreen. In fact, a few years ago, a contact at the North Korean Mission at the UN confided, “Mr. Carlin is able not only to read between the lines of Pyongyang statements, but he also reads between the words.”


By tracking the nuclear and political developments side by side, how they intersected or diverged, it became clear that Pyongyang has followed a dual-track strategy of diplomacy and nuclear development. I was able to identify a number of key events—“hinge points” I call them—in which Washington failed to weigh the risks and rewards presented by a particular combination of diplomatic and technical factors. Contrary to the prevailing view in Washington that North Korea only used diplomacy to buy time for its nuclear program, it was Kim Il Sung, the country’s founder, who, in the early 1990s, seriously explored a long-term strategic relationship with the United States through diplomacy. Whereas accommodation with Washington was in his view the best path to survival given the dramatic geopolitical upheavals at the end of the Cold War, a time when North Korea felt abandoned and even threatened by both Russia and China, Kim Il Sung insisted such accommodation be based on the projection of strength, not weakness.8

By this time, North Korea’s economy and conventional military were increasingly falling behind South Korea’s and, of course, the North was heavily outmatched by the United States. The only projection of strength would have to come from the North’s nuclear program, making it a top priority for the regime. By choosing to pursue diplomacy plus nuclearization, not one or the other, North Korea has been able to hedge against failure in one track or the other and mitigate the risks inherent in the vicissitudes of the post–Cold War international system and its own authoritarian domestic politics.

North Korea’s determination to build a nuclear weapon option to deter a United States that remained the North’s central adversary was resolute, if not always predominant. Pyongyang has alternated prioritizing one track or another over the last thirty years but has not made the strategic decision to irrevocably commit to a single track. While the North has slowed its nuclear progress at times, it has never fully abandoned the nuclear track. But the realization and permanent pursuit of a credible nuclear deterrent were not necessarily preordained, despite the attention and resources that North Korea has devoted to its nuclear development. By leaving open the possibility of success in either track and taking advantage of the flexibility this afforded them in their dealings with the United States, the Kims have sought a measured degree of insurance for the long-term survival of the country and the regime. In other words, each of the Kims at times seriously pursued diplomacy to reach strategic accommodation with Washington, which in turn opened the way for agreements that would retard further development of the nuclear weapons program.

Washington, however, had a singular focus on denuclearization. It ruled out a political middle ground by forcing Pyongyang early on to choose between diplomacy or the nuclear program. It failed to deal with Pyongyang’s dual-track strategy, missing key opportunities for diplomacy and misinterpreting some of the North’s actions, which led to bad decisions—the hinge points I mentioned above. The resulting bad decisions by Washington had bad consequences, leading to a state of nearly continuous crisis for twenty years and one of the greatest security risks the United States faces today.

Washington consistently failed to recognize and/or cope effectively with North Korea’s dual-track strategy. The North was often moving on two parallel fronts—the technical/military front to build a nuclear arsenal or earn foreign currency through nuclear or missile exports and the engagement/diplomacy front to explore strategic accommodation with the United States. Even when Washington suspected that the North was moving on parallel tracks, it did not deal effectively with Pyongyang. Washington’s North Korea policies seldom incorporated sound technical analysis, either because such analysis was not sought out by the policymakers or because it was contrary to Washington’s policy assumptions and political priorities.

The logic guiding the North’s dual-track strategy is pragmatic and has steadied the hand of Pyongyang as the mantle of leadership passed down from founder Kim Il Sung upon his death in 1994 to his son Kim Jong Il, and to his grandson Kim Jong Un, in 2011. All three Kims have, to different degrees, found it useful to implement elements of the dual-track strategy. On the one hand, diplomatic engagement could normalize relations with North Korea’s chief antagonist, the United States, neutralizing an outsized military threat, counterbalancing against regional competitors, and potentially freeing up resources to concentrate on the economy. On the other hand, the acquisition of a nuclear arsenal could also neutralize the threat of the United States and its regional allies via different means: deterring and protecting the regime from aggressive neighbors and an implacably hostile United States. Equally or perhaps more importantly, the strength of a nuclear arsenal could force Washington to take Pyongyang seriously, to deal with it on the diplomatic track.

Pyongyang realized long ago that to develop the technical foundations for nuclear and missile programs requires time and significant resources. To succeed, the North pursued these programs with great tenacity, although at times the pace and extent were contingent on what was achievable on the diplomatic front. I believe that each of the Kim regimes had a genuine interest in diplomacy, beginning with Kim Il Sung’s strategic vision of normal relations with the United States. Over the years, his son and grandson also explored such strategic accommodation at times. All three, however, believed that while exploring diplomacy, nuclear weapons could not be relinquished until accommodation had been achieved to their satisfaction.

At some key decision points, Pyongyang accelerated the nuclear hedge too soon instead of giving diplomacy more time to bear fruit. Whereas technical development is subject to the laws of physics, diplomacy can change reality as it progresses. What is impossible today often becomes conceivable tomorrow. Even if the Kims believed they wouldn’t abandon their weapons at any given moment, it is possible to imagine and work toward circumstances in which they may view it in their best interest to do so. Unfortunately, decisions at each hinge point facilitated the North’s almost unfettered expansion of its nuclear and missile programs, making a path to the elimination of such weapons increasingly difficult. Nevertheless, declaring that Kim Jung Un will never give up his weapons is counterproductive. We simply don’t know—and likely, neither does he.


In Hinge Points, I take the reader on a journey that tracks the nuclear and political developments side by side, how they intersected or diverged over the past twenty years. The journey is complex but ultimately necessary to see what I saw, hear what I heard, and understand what, in my view, best explains one of Washington’s greatest foreign policy failures. The reader doesn’t have to be a nuclear scientist or an expert in nuclear weapons to grasp the interplay between diplomatic and technical developments. In the early chapters I provide an inside view of the North’s nuclear complex and its technical staff based on my seven visits. Meetings with North Korean diplomats convinced me that they were able to integrate technical and diplomatic developments, in stark contrast to what happened in Washington from the George W. Bush administration through the Trump years. The chapters describing the seven visits are separated by chapters that analyze the political climate, particularly as it played out in Washington and Pyongyang, to highlight the importance of following both technical and diplomatic developments. The political analysis is not meant to constitute a diplomatic history or a detailed description of the negotiations process during the past twenty years.9

After describing my last visit to North Korea in 2010, I continue to integrate the technical analysis with the political and diplomatic developments chronologically through the Obama and Trump administrations. I describe the hinge points that took us further and further down the road to a North Korea with a growing, and more sophisticated, nuclear arsenal. Both Washington and Pyongyang squandered opportunities. In many of these cases, had Washington properly incorporated a sensible risk analysis of the technical factors into policy decision-making, it may have been able to implement a reliable long-term process to freeze, roll back, and eventually eliminate the North’s nuclear program, rather than see it advance.

The tragedy, in my view, is that Washington, no matter who was in the White House, failed to conduct a technically informed risk/benefit analysis. Instead, American political leaders and policymakers made decisions that let political or ideological prejudices win out over decisive analysis. Over and over, these political decisions that failed to incorporate a clear-eyed evaluation of their technical consequences opened the door for North Korea to expand its nuclear program. Political leaders in Washington relied on their own (often misguided) assumptions about North Korea’s motivations for developing its nuclear program and engaging in diplomacy. Many American policymakers have resisted engagement with the Kim regimes on what they cite as moral grounds: These reigns were considered reprehensible with horrendous human rights violations, and they were likely to cheat on every agreement reached. Washington’s policies were also hampered by the corrosive effects of differing and dueling ideologies, poisonous disagreements and infighting within administrations, and a lack of continuity within and across U.S. administrations. Similar mistakes were made over and over. While North Korea’s leadership remained focused as it transitioned from one Kim to another, Washington vacillated.

I acknowledge that over the years many issues have plagued U.S. decision-making about the North Korea nuclear question. These issues have been debated by politicians, documented by scholars, and examined in the news media and scores of books. I benefited from reviewing memoirs, commentaries, and scholarly works. This book focuses on two primary failings that have received little attention: first, the absence of full recognition of North Korea’s dual-track strategy to pursue diplomacy and nuclear development; second, Washington’s seeming inability to incorporate technically informed risk/benefit analysis in its decision-making.

The nuclear issue is, of course, not the only one that impedes peace and security on the Korean Peninsula, but it continues to cast a larger and darker shadow over everything else as the North’s arsenal grows more and more dangerous. Thus, I focus on the nuclear issue because its resolution is necessary, although I realize not sufficient, to resolve decades of enmity.


1. Frank Pabian, Joseph S. Bermudez Jr., and Jack Liu, “North Korea’s Punggye-ri Nuclear Test Site: New Media Reports of an Imminent Sixth Test Again Cannot Be Corroborated,” 38 North (August 30, 2017), 2017/08/punggye083017/

2. Earthquake Hazards Program, “M 6.3 Nuclear Explosion—21 km ENE of Sengjibaegam, North Korea,” USGS (September 3, 2017), earthquakes/eventpage/us2000aert/executive#executive; CTBTO estimate was magnitude of 6.1. See Technical Findings, “3 September 2017: North Korea Announced Nuclear Test,” CTBTO (September 7, 2017, updated April 12, 2018), the-treaty/developments-after-1996/2017-sept-dprk/technical-findings/

3. David Sanger and Choe Sang-Hun, “North Korean Nuclear Test Draws U.S. Warning of ‘Massive Military Response,’New York Times (September 2, 2017), 2017/09/03/world/asia/north-korea-tremor-possible-6th-nuclear-test.html

4. Dimitri P. Voytan, Thorne Lay, Esteban J. Chaves, and John T. Ohman, “Yield Estimates for the Six North Korean Nuclear Tests from Teleseismic P Wave Modeling and Intercorrelation of P and Pn Recordings,” JGR: Solid Earth 124, no. 5 (May 2019): 4916–4939, 10.1029/2019JB017418

5. David Wright, “North Korea’s Longest Missile Test Yet,” All Things Nuclear (November 28, 2017), dwright/nk-longest-missile-test-yet

6. Pritchard published a memoir of his government service work in North Korea. Charles L. Pritchard, Failed Diplomacy (Washington, DC: Brookings Institution Press, 2007). Carlin co-authored the third edition of the classic The Two Koreas: A Contemporary History with Don Oberdorfer (New York: Basic Books, 2014). Lewis published several influential books on China. For instance, see John Wilson Lewis and Xue Litai, China Builds the Bomb (Stanford: Stanford University Press, 1988).

7. Over the years the Stanford University team consisted of affiliates Chaim Braun, Nick Hansen, Frank Pabian, and Allison Puccioni, and former students Niko Milonopoulos, Sulgiye Park, and Elliot Serbin.

8. Mike Chinoy, Meltdown: The Inside Story of the North Korean Nuclear Crisis (New York: St. Martin’s Griffin, 2009), 3. (Chinoy’s assessment of what Kim Il Sung said at a Pyongyang meeting he attended with evangelist Billy Graham).

9. The reader is referred to detailed histories such as Joel S. Wit, Daniel B. Poneman, and Robert L. Gallucci, Going Critical: The First North Korean Nuclear Crisis (Washington, DC: Brookings Institution Press, 2004), addressing the early years of the crisis; Mike Chinoy’s Meltdown for the Clinton years; and Oberdorfer and Carlin’s Two Koreas for a comprehensive history through 2012.