Over the last three months, North Korea has tested an advanced fission device more powerful than its previous nuclear tests, as well as its long range Hwasong-14 missile. While there was some disagreement over whether that test represented a nascent intercontinental ballistic missile (ICBM) capable of hitting the continental United States, North Korea is clearly making progress in designing long-range missiles and miniaturizing its nuclear weapons to fit on those missiles.

The rate and extent of North Korea’s capabilities has surprised most academics and outpaced the predictions of many policymakers. A recent Washington Post article describes analysts and policymakers as having “been surprised repeatedly.” Vipin Narang and Nicholas Miller – two top scholars of nuclear weapons – argue that, according to most academic theories, “North Korea was never supposed to get the bomb.” As a poor, backward country, and given the difficulties personalist, autocratic states have at managing large-scale complicated projects, North Korea should not have the capabilities that it has today.

Why has the dominant reaction been surprise? One reason could be the tendency to look at nuclear weapons in isolation. Scholars have studied and assessed nuclear weapons separately from other military technologies because their effect is so outsized relative to that of other weapons. A belief in the nuclear revolution – the unique importance of nuclear weapons – underlies this approach.

Expanding the analytical horizon to think about nuclear weapons in the context of other military technologies reveals a story that can help us understand North Korea’s success. Nuclear weapons and missiles are now relatively old technologies. The surprising thing, in the scope of military history, is how limited proliferation has been. By understanding how the nuclear proliferation process is similar to and different from the diffusion of other weapon systems, we can improve our knowledge of nuclear and missile proliferation, and better predict the next North Korea.

What’s So Special About Nuclear Weapons?

The international community has treated nuclear weapons as special almost from the dawn of the nuclear age. From Bernard Brodie’s The Absolute Weapon, published in 1946, to Robert Jervis’s The Meaning of the Nuclear Revolution and more recent studies, scholars and policymakers tend to treat nuclear weapons as a category distinct from all other weapons due to fear of the unique consequences of nuclear war. This means they also treat the development process for nuclear weapons as unique. Arguments over security, economic, political, and other factors that drive nuclear proliferation generally occur in a vacuum, rather than by relating proliferation to how other weapons spread.

Similarly, over time the international community has built an entire infrastructure around preventing nuclear and long-range missile proliferation that is more complete than that used to address any other weapon system. This infrastructure includes treaties such as the Nuclear Non-Proliferation Treaty, agreements such as the Nuclear Suppliers Group and Missile Technology and Control Regime, other efforts including the U.S.-led Proliferation Security Initiative, and efforts to generate economic costs for pursuing nuclear weapons, such as sanctions imposed by the United Nations or individual states.

Because of all this, countries have to overcome a large-scale economic price tag and international condemnation to build nuclear weapons and an ICBM, which makes them less likely to try, or try hard, in the first place. Nuclear powers also have carrots designed to make nuclear weapons less attractive to potential proliferators. Security guarantees by a nuclear power can reassure a would-be proliferator, as the United States does with Japan. Opportunities for global economic engagement can tempt leaders who wish to make their countries wealthier away from the nuclear path.

When that infrastructure fails, however, we are left with a question: How hard is it actually for a determined proliferator to acquire nuclear weapons? The answer? Not as hard as you might expect. And this becomes clearer when you think about the acquisition of nuclear weapons in the context of other military technologies.

For conventional military technologies such as tanks, fighter aircraft, submarines, or guided munitions, determined adopters generally prove capable of either acquiring a capability or at least something close. Countries mimic, reverse-engineer, and otherwise generally figure out how to adopt or counter the capabilities of other nations. The financial costs, the technological complexity, and the organizational challenges involved in adopting a technology, whether nuclear or not, can influence the rate of diffusion.

What do these challenges look like when considering the case of nuclear weapons? In my book, The Diffusion of Military Power, I argue that, putting aside international institutions designed to prevent proliferation, nuclear weapons also require a huge financial investment and are not dual-use, meaning there are no readily adaptable commercial variants. Nuclear weapons themselves are also technically complicated to build, requiring substantial infrastructure as well as enriched uranium or plutonium.

Yet there are two things about the development process for acquiring nuclear weapons, understood in relation to “normal” military technologies, that help explain how North Korea was able to acquire both nuclear weapons and long-range missiles despite those constraints. These insights are missed when a focus on the unique destructive power of nuclear weapons leads us to examine how these weapons are developed in isolation, rather than looking at the proliferation process in relation to the spread of other weapons.

First, nuclear weapons are the only military technology in history where having the oldest and most primitive version of the capability still has significant implications, because of their destructive effects. And nuclear weapons are old technology. Countries have built nuclear weapons for more than 70 years, and ICBMs for more than 50 years. Compare this to another weapon system: Imagine if North Korea invested for 40 years to build capabilities equivalent to the first aircraft carrier in history, the HMS Furious, deployed by the Royal Navy in 1917. That investment would yield nothing more than a floating target for any competent national military. But that’s essentially what North Korea has done with its nuclear program – it’s worked since before the end of the Cold War to achieve what the United States and Soviet Union accomplished decades before – and now its success is reshaping the international security environment in the Asia-Pacific.

Second, because even old or less sophisticated versions of nuclear weapons and long-range missiles have strategic consequences, as I wrote, investments in nuclear weapons or missiles are cumulative. Knowledge, equipment, and infrastructure for nuclear and missile capabilities can accumulate over decades without becoming obsolete. Countries merely need to aggregate the technology to the point of surpassing a decades-old bar.

North Korea, in essence, put its nickels in a jar every year for 40 years and eventually gained an extremely useful capability. This unique facet of nuclear weapons actually makes their proliferation easier, not harder, than developing advanced conventional weapon systems. The fear of obsolescence due to technological change, or concern about the ability of an organization to effectively employ a weapon system, can discourage countries from pursuing advanced conventional weapons or make them less likely to succeed in that pursuit. That fear of obsolescence does not exist for nuclear weapons.

These issues, in combination with the general diffusion of knowledge and know-how, may reduce the fundamental adoption requirements for nuclear weapons over time. In the language of theories of innovation, there are late-mover advantages to nuclear acquisition. This may also help explain Joshua Pollack’s recent point about how gross domestic product is not determinative in predicting nuclear acquisition.

We can gain relevant insights about North Korea’s success by examining the challenges of acquiring nuclear weapons versus those of obtaining more “normal” military technologies.

Explaining the North Korean Case

The international infrastructure designed to prevent nuclear proliferation generally works very well. However, when the international constraints on nuclear proliferation are stripped away, we are left with decades-old technology whose design principles are relatively well-known. From this perspective, North Korea’s proliferation success becomes much less surprising.

Of course, this all appears clearer in hindsight. When I previously examined nuclear weapons as a military innovation, for example, I did not anticipate North Korea’s success, nor did I incorporate its efforts to overcome international constraints on proliferation. My model also showed industrial capacity as critical to proliferation success. And despite highlighting the same data that Pollack recently used, I failed to take the argument to its logical conclusion and instead focused on the size of the technical hurdles to acquire nuclear weapons.

Moreover, simply importing “normal” military technology diffusion models, while helping us understand North Korea, would probably overpredict proliferation in general, particularly in light of international efforts to make weapons acquisition harder. States such as Iraq and Libya tried but failed to acquire nuclear weapons. Large barriers do exist, especially for more economically backwards countries. But perhaps scholars and policymakers read the lessons of Iraq and Libya too deterministically, rather than probabilistically, in thinking about North Korea, especially given that the country proved better than other potential proliferators at circumventing international restrictions on access to technology.

Understanding the Present and Future of Nuclear Proliferation

To be fair, some studies of nuclear proliferation have weathered the North Korean case better than others. Those who believe supply-side support is critical to bomb development might point to Russia’s early aid to North Korea’s nuclear program. More than a decade ago, Etel Solingen pointed out that countries who fear or do not value global economic integration are more likely to proliferate – a description that seems to characterize North Korea.

We rarely observe countries actually pushing hard to acquire nuclear weapons, meaning researchers and policymakers risk drawing broad inferences from too few cases. What happens when interlocking formal and informal international institutions fail to dissuade a country from pursuing nuclear weapons (because they do not fear the costs of nuclear pursuit and/or do not want the benefits of global economic integration), and fail to cut off all avenues of potential assistance? This is what happened with North Korea. The result is something that looks a lot more like what we would see with the diffusion of “normal” decades-old military technologies: acquisition.

But the cumulative nature of nuclear investments and the utility of older nuclear and missile technology mean that if a country is determined to acquire nuclear weapons, success should be quite plausible. Not every state will succeed, of course, but neither is an outcome like what we see with North Korea shocking. Bringing these strands of thinking together can more accurately explain the nuclear and long-range missile proliferation patterns of today and tomorrow.

Michael C. Horowitz is professor of political science and the associate director of Perry World House at the University of Pennsylvania. He is also a senior editor at War on the Rocks. You can find him on Twitter @mchorowitz.

Image: U.S. Army/Edward Johnson