Kenneth Waltz died this week, just shy of his 89th birthday. I can’t say that I knew the famous Berkeley scholar well, though I did once have lunch with him early in my career. It was a harrowing experience for me as he challenged me about why I thought the Third World mattered. I learned later that my noontime grilling was nothing compared to the tough love he gave his students, who invariably remember him with deep respect and affection but also still present some of the symptoms of post-traumatic stress disorder.

But what all of us in the field of international relations experienced on a regular basis was the power of Waltz’s intellect, which towered over the discipline and inspired all of us who inclined toward a realist approach with his application of rigorous theory to the most important practical issues statesmen grappled with.

Waltz’s scholarly stature was due entirely to the force of his intellect and his willingness to challenge prevailing orthodoxies. He never served in government. And while his writings touched on many of the major events of the day—Vietnam, nuclear proliferation, the Cold War—he did not aspire to be a public intellectual.

Instead, Waltz made his mark through a handful of books and articles in which he advanced simple, yet counterintuitive, theories about how international politics works. His theories often struck other scholars as implausible at first, but their logic often proved irresistible over time. And when he applied his theoretical insights to the real world, they regularly made sense of some otherwise puzzling things.

Waltz wrote three major books, but his magnum opus was his 1979 Theory of International Politics, which is widely regarded as the urtext of modern Neorealism. In it, Waltz employed a unique combination of political theory (his surprising debt to Immanuel Kant would make a great doctoral dissertation) and modern economic reasoning to produce a system-level theory of international relations.

In contrast to the dominant “reductionist” theories of international relations that focused on traits within individual states to explain their behavior, Waltz offered a theory of international relations based upon factors at the level of the system itself. For example, he argued that the number of major powers (the distribution of capabilities), rather than their culture or the nature of their political systems, determined the stability of the system.

Waltz was, of course, not the first theorist of international relations to explore how the system’s “polarity” affected its dynamics, but his was the most logically rigorous of all such theories. He also maintained, in contradiction to many other systems theorists, that the most unstable systems were those with three or more powers (multipolarity) or those with only one power (unipolarity).

Indeed, he is famous for his argument about the stability of a bipolar world. In a 1964 article, written at the height of the Cold War, Waltz argued that the U.S.-Soviet rivalry was likely to be stable on two grounds: Such a configuration of power would reduce uncertainty because the two great powers had to focus only on each other. And bipolarity also lessened conflict because each of the poles would rely mainly on its own internal resources to balance the other, eliminating the need to compete with each other over third parties. From our post-1989 perspective, the “long peace” of the Cold War may have seemed inevitable, but Waltz advanced this radical argument just two years after the Cuban Missile Crisis.

Like many college professors, Waltz became skeptical of growing U.S. involvement in the war in Vietnam. Of course, he was not the only, or even the most prominent, realist critic of the war. That distinction would go to the University of Chicago’s Hans Morgenthau. But whereas Morgenthau’s critique of the Johnson administration’s policies in Vietnam was that they were ill-advised from the standpoint of U.S. national interests, Waltz offered a more systematic assessment of precisely why that was the case.

Waltz’s structural perspective led him to conclude that Vietnam, and indeed most other parts of the Third World, were not a decisive element in the larger U.S.-Soviet rivalry because bipolarity encouraged internal, rather than external balancing. This conclusion followed ineluctably from his structural theory of international politics. It was also prescient: Despite the United States “loss” of South Vietnam in 1975, the balance between the two was hardly upset by the loss of this part of the Third World.

One could fairly complain that Waltz’s arguments about the stability of a bipolar world lulled realists into a false sense of complacency about the perpetuation of the Cold War. This may have resulted from what a younger realist critic calls Neorealism’s “status quo bias.” Yet even here Waltz anticipated that the Cold War was likely to end via Soviet exhaustion. As he wrote in Theory of International Politics, “With half our GNP, [the Soviet Union] has to run hard to stay in the race. One may think the question to ask is not whether a third or fourth country will enter the circle of great powers . . . but rather whether the Soviet Union can keep up.”

Despite its alleged failure to anticipate the end of the Cold War, Waltz’s structural theory was also relevant to the post-Cold War debate about U.S. primacy. Whereas Waltz saw bipolarity as stable and enduring, the logic of his structural theory led him to predict that the U.S.’s “unipolar moment” was likely to be fleeting because other states would eventually balance against us.

Scholars continue to debate whether Waltz was correct about the lack of durability of unipolarity, but there is mounting evidence that the world is beginning to push back. More presciently, Waltz predicted that the absence of a counterbalance in unipolarity would lead to trouble for the hegemon itself. It seems unlikely that the United States would have over-reached as it did in Iraq and Afghanistan if it faced another peer competitor.

But Waltz’s most controversial argument highlighted the positive benefits of nuclear proliferation. From the very beginning of the nuclear age, preventing the spread of the ultimate weapon to other powers was something that united the dovish atomic scientists and the hawkish nuclear strategists.

In a widely debated 1981 monograph published by the International Institute of Strategic Studies, Waltz laid out an argument for why “more may be better” in the nuclear realm. The icy logic undergirding this conclusion was simple: Nuclear weapons were useful only to deter attacks on the great powers’ homelands, and so the security dilemma caused by international anarchy could be resolved with each state acquiring a secure second-strike capability.

One of Waltz’s former colleagues recounts a story (perhaps apocryphal) about a conference soon after the Iranian Revolution, when Waltz was asked if he thought even the mad mullahs of Iran could be trusted with nuclear weapons. Supposedly, his response was “no.”

But in one of his last major articles in Foreign Affairs just last summer, Waltz stood by his theoretical convictions and presented his brief for “Why Iran Should Get the Bomb.” Waltz never shied away from taking bold and controversial positions, and this particular one generated a lot of debate.

Yet when we look back over the course of nuclear history at the actual results of rogue states acquiring nuclear weapons, the apocalyptic rhetoric of Waltz’s critics seems overdrawn. If Mao’s China, wracked by internal conflict taking millions of lives and led by a dictator who said the most hair-raising things about nuclear war, could still behave responsibly as a nuclear power, Waltz’s sanguine view of an Iranian nuclear capability was hardly beyond the pale.

Waltz’s passing is a sad moment for his family and friends. For the rest of us it is an opportunity to appreciate his enduring intellectual contributions to the study of international relations. The most important of these, in my opinion, was his demonstration of the power of theory in helping us make sense of a complicated world and to think intelligently about how to deal with it.

Michael C. Desch is professor and chair of the Department of Political Science at the University of Notre Dame.

Image: theory-talks.org/Peer Schouten