Security Dilemmas & Nuclear Proliferation

Overview

On February 5, 2026, the New START treaty expired. It was the last remaining agreement limiting the number of nuclear weapons the United States and Russia can deploy. For the first time in over fifty years, there are no binding limits on the world’s two largest nuclear arsenals. The architecture that kept the Cold War from becoming a hot war — the treaties, the inspections, the verification regimes — has been steadily dismantled. The INF Treaty collapsed in 2019. Russia suspended New START in 2023. And now it is gone entirely.

The U.S. and Russia together hold roughly 90 percent of the world’s nuclear weapons — about 12,000 warheads between them. China is in the middle of the most rapid nuclear expansion since the Cold War and may triple its arsenal by 2035. North Korea has tested ICBMs that can reach North America. Pakistan has the fastest-growing nuclear stockpile in the world.

So: should we be worried? Or does the fact that no nuclear weapon has been used in conflict since 1945 tell us that deterrence works — that the bomb actually keeps the peace?

This module puts the theoretical frameworks from Module 1 to work on one of the most consequential questions in international politics. By the end, students can explain why states pursue nuclear weapons through multiple analytical lenses and take an informed position in the central proliferation debate.

The Security Dilemma

The security dilemma is one of the most important concepts in IR — and one of the most counterintuitive. It describes a situation in which one state’s efforts to increase its own security make other states less secure, triggering an action-reaction spiral that leaves everyone worse off.

The logic is straightforward. Under anarchy, states cannot be certain of each other’s intentions. When State A builds up its military capabilities — even for purely defensive reasons — State B cannot know that those capabilities won’t be turned against it. So State B responds by building up its own forces. State A sees this as confirmation that State B is a threat, and arms further. Neither side intended conflict. Both end up in an arms race.

The nuclear dimension amplifies this dynamic. During the Cold War, the U.S. and Soviet Union went from a handful of nuclear weapons in the late 1940s to a combined stockpile of approximately 70,000 warheads by the mid-1980s. Each new weapon system — MIRVed warheads, submarine-launched missiles, precision guidance — was justified as a necessary response to the other side’s capabilities. The result was a balance of terror that nearly broke down on multiple occasions.

The 1962 Cuban Missile Crisis is the canonical example.
The 1983 Soviet false alarm — when a satellite malfunction indicated incoming U.S. missiles, and only the judgment of duty officer Stanislav Petrov prevented a retaliatory launch — is arguably the more chilling one.
In 1961, a U.S. B-52 carrying two hydrogen bombs broke apart over North Carolina; one bomb’s arming sequence progressed through all but one of its safety interlocks.

These incidents are not aberrations. They are what the security dilemma produces when the stakes are existential.

The Proliferation Debate: Waltz vs. Sagan

The central intellectual debate of this module asks a deceptively simple question: does the spread of nuclear weapons make the world safer or more dangerous?

The Optimist: Kenneth Waltz

Kenneth Waltz (1981) argued that nuclear proliferation increases stability. His position, summarized as “more may be better,” rests on the logic of deterrence:

Nuclear weapons make the cost of war catastrophic and obvious. When both sides possess them, neither can rationally initiate conflict.
The historical record supports this: no two nuclear-armed states have ever gone to war with each other. The “long peace” of the Cold War — the longest period without great-power war in modern history — coincided with the nuclear age.
Even between rivals like India and Pakistan, nuclear weapons appear to have imposed caution. Crises that might have escalated to full-scale war in a pre-nuclear era have been contained.
The clarity of nuclear deterrence reduces the risk of miscalculation. Leaders know exactly what is at stake.

Waltz’s position is provocative precisely because it runs counter to common intuition. But it has a cold logic: if the purpose of military power is to prevent war, then the weapon that makes war most catastrophic is also the one that most reliably deters it.

The Pessimist: Scott Sagan

Scott Sagan (1996) argues that nuclear proliferation increases danger. His position, “more will be worse,” rests on a fundamentally different set of assumptions about how states actually behave:

Waltz’s argument assumes rational, unitary state actors. Sagan argues this is naive. Real states are not monolithic decision-makers. They are complex organizations with competing bureaucratic interests, information asymmetries, and communication failures.
Organizational pathologies make accidents, unauthorized use, and miscalculation far more likely than rational deterrence theory admits. Military organizations develop standard operating procedures optimized for offensive readiness, not cautious restraint.
Preventive war incentives arise during the transition period when a state is acquiring nuclear weapons but has not yet achieved a secure second-strike capability. Adversaries have a window of opportunity to strike first.
Civil-military tensions in new nuclear states may mean that political leaders lack effective control over nuclear forces. The command-and-control infrastructure that the U.S. and Soviet Union developed over decades does not come automatically.

The near-misses — Petrov in 1983, North Carolina in 1961, the 1995 Norwegian rocket incident — are not anomalies in Sagan’s framework. They are predictable consequences of complex organizations managing existential weapons under conditions of uncertainty.

Sagan’s Three Models

Beyond the optimist/pessimist debate, Sagan provides a framework for understanding why states build nuclear weapons in the first place. His 1996 article identifies three distinct models, each with different causal logics and policy implications.

The Security Model

The most intuitive explanation. States build nuclear weapons in response to external security threats — particularly threats from nuclear-armed adversaries or conventional military superiority that cannot be matched by other means.

Logic: A state facing an existential security threat acquires nuclear weapons to deter attack.
Key actors: State leaders making strategic calculations about survival.
Case example: The Soviet Union’s crash program after the U.S. bombings of Hiroshima and Nagasaki (1945–1949). Facing an American nuclear monopoly, the USSR had overwhelming security incentives to develop its own arsenal.
Policy implication: Reduce security threats and states will have less reason to pursue nuclear weapons. Security guarantees, alliance commitments, and arms control agreements are the appropriate tools.

The Domestic Politics Model

States build nuclear weapons because powerful domestic actors — military organizations, nuclear energy establishments, and political elites — have bureaucratic, economic, or political interests in pursuing them, regardless of the external security environment.

Logic: Nuclear weapons programs create jobs, prestige, and institutional power. Once a nuclear establishment exists, it lobbies for continuation and expansion.
Key actors: Military bureaucracies, defense scientists, nuclear energy agencies, political leaders seeking nationalist legitimacy.
Case example: France’s nuclear program under de Gaulle. Security threats alone do not explain the decision — France was already protected by NATO and the U.S. nuclear umbrella. But the French nuclear establishment, combined with de Gaulle’s vision of national grandeur and independence, drove the program forward.
Policy implication: Look inside the state. International security assurances alone may not be sufficient if domestic constituencies have independent reasons to pursue the bomb.

The Norms Model

States build (or refrain from building) nuclear weapons because of international norms about nuclear status, prestige, and identity. Nuclear weapons carry symbolic meaning beyond their military utility.

Logic: Possessing nuclear weapons signals modernity, technological sophistication, and great-power status. For some states, nuclear weapons are badges of national prestige. For others, non-proliferation norms create a strong taboo against acquisition.
Key actors: National identity, international prestige hierarchies, norm entrepreneurs.
Case example: India’s 1974 “Peaceful Nuclear Explosion.” India framed its test as a demonstration of technological capability and civilizational achievement — a statement about India’s rightful place in the world, not just a response to China’s nuclear arsenal.
Policy implication: Strengthen non-proliferation norms. The NPT, the nuclear taboo, and the stigma against testing all contribute to a normative environment that discourages proliferation.

The multicausality conclusion: Sagan argues that these models are not mutually exclusive. Most proliferation decisions involve a combination of security pressures, domestic political dynamics, and normative considerations. The analytical skill is identifying which factors are dominant in each case — and recognizing that single-cause explanations are almost always insufficient.

Beyond Sagan

Subsequent scholars have extended and complicated Sagan’s framework:

Jacques Hymans (2006) introduced psychological and identity variables. He argues that proliferation decisions are driven by a specific combination of leader psychology: “oppositional nationalism” — leaders who define their nation’s identity in opposition to a specific external enemy and who possess high levels of personal confidence. This explains why some threatened states pursue nuclear weapons while others in similar security environments do not.

Etel Solingen (2007) focuses on political economy and regime type. She argues that states with outward-oriented, internationally integrated economic coalitions are less likely to pursue nuclear weapons because the costs (sanctions, isolation) are too high. Inward-looking, nationalist regimes face lower economic costs and higher political rewards from nuclearization.

Johnson, Kartchner, and Larsen (2009) introduce strategic culture — the idea that deeply embedded cultural beliefs about the role of force, the nature of conflict, and the meaning of security shape how states relate to nuclear weapons. A state’s strategic culture filters how it perceives threats and what responses it considers legitimate.

These extensions do not replace Sagan’s models but deepen them — adding psychological, economic, and cultural dimensions to the security/domestic/norms framework.

Case Study: North Korea

North Korea is the integrative case that ties the models together. Every explanation has something to contribute, and no single model is sufficient:

Security model: North Korea faces a genuine existential security threat. It confronts the U.S. military presence in South Korea, joint U.S.-ROK military exercises, and regime-change rhetoric from Washington. From Pyongyang’s perspective, nuclear weapons are the ultimate insurance policy against invasion.
Domestic politics model: The Kim regime uses the nuclear program to consolidate internal power. Byungjin — the policy of parallel development of nuclear weapons and the economy — positions the regime as delivering both security and prosperity. The nuclear establishment is deeply embedded in the state apparatus, and the program’s continuation serves regime survival regardless of external conditions.
Norms model: Nuclear weapons are central to North Korean identity and regime legitimacy. The DPRK’s constitution was amended to enshrine its nuclear status. The program is framed domestically as the crowning achievement of juche (self-reliance) — a demonstration that a small, isolated state can stand against the world’s most powerful military.
Bargaining leverage: Beyond Sagan’s original three models, North Korea has also used its nuclear program as a bargaining chip — leveraging it for diplomatic attention, economic concessions, and sanctions relief. The program’s value extends beyond security into diplomacy and regime maintenance.

The lesson: any analysis of North Korean nuclearization that relies on only one model will be incomplete. The security dimension is real but does not explain the timing, intensity, or symbolic investment in the program. The domestic and normative dimensions fill those gaps.

The Framing Experiment

This module includes a live framing experiment. Students are randomly assigned to read a passage framing nuclear weapons as a stabilizing force, an existential threat, or a neutral overview — then answer the same questions about nuclear safety. The results show that the Waltz–Sagan debate maps onto a genuine perceptual split that can be induced by a single paragraph of narrative framing.

See the full experiment design, methodology, and illustrative results on the Experiments page.