Leiden University · BA International Studies Teaching International Relations

Lecture 2 · Course week 3

Security Dilemmas and Nuclear Proliferation

Why states build the bomb

The lecture asks why states acquire nuclear weapons and how their choices affect security. Deterrence may prevent attack, intensify insecurity or fail through accident and organizational error.

Date
16 February 2026
Format
Two-hour lecture
Instructor
Steven Denney
  • Security dilemma
  • Deterrence
  • Proliferation
  • North Korea

Overview

The security dilemma provides the starting point for explaining nuclear proliferation. Measures intended to protect one state can make others less secure. The resulting action and reaction may drive an arms race even when neither side seeks war. The lecture then separates deterrence from proliferation. It also distinguishes horizontal from vertical spread and a secure second-strike capability from mere possession.

Scott Sagan’s three models organize the explanation of acquisition. States may seek nuclear weapons in response to external threats. Domestic organizations and political coalitions may also favor them, while the bomb can carry status and normative meaning. The North Korean case shows how these mechanisms can operate together. The lecture then stages the Waltz–Sagan dispute over whether proliferation stabilizes international politics. It closes with the NPT and the limits of safeguards and arms control.

Questions guiding the lecture

  1. Why do states build nuclear weapons, and which mechanisms distinguish Sagan's three models?
  2. When does deterrence produce stability, and when can uncertainty, accidents, or organizations undermine it?
  3. How does the North Korean case combine security, domestic, and normative motives?
  4. What can the NPT and arms-control institutions accomplish when states retain strong security incentives?

Lecture map

Part 1

The path from the security dilemma to deterrence runs through uncertainty and arms racing. Second-strike capability and mutual assured destruction define the conditions for credible restraint.

Part 2

Sagan explains acquisition through security, domestic politics and norms. Psychological and political-economic accounts extend the framework, as does work on strategic culture.

Part 3

Students use North Korea as a multicausal case and assess where each model adds explanatory value.

Part 4

The Waltz–Sagan debate asks whether more nuclear weapons make the world safer. The section then examines the nonproliferation regime and contemporary pressure on verification and restraint.

Readings

Required · map

Whitham, Ben, and Andrew Heywood. 2023. Global Politics, 3rd ed., Chapter 12, “The Global Politics of Weapons of Mass Destruction.”

Introduces weapons of mass destruction, deterrence, proliferation, arms control, and the normative debate.

Required · theory

Sagan, Scott D. 1996–97. “Why Do States Build Nuclear Weapons? Three Models in Search of a Bomb.” International Security 21(3): 54–86.

Provides the lecture's causal framework. Track the observable implications of each model because their value extends beyond the labels themselves.

Recommended extensions

The syllabus recommends Sheena Chestnut Greitens on WMD proliferation, Sang-Hun Choe on North Korea's arsenal, and Heather Williams on changes in Russian nuclear doctrine. Together they extend the core models into contemporary institutions and cases.

Classroom study

Randomized survey experiment

Framing nuclear safety

The study asks whether a deterrence-and-stability brief or a danger-and-near-miss brief changes assessments of nuclear stability relative to a descriptive control.

Qualtrics evenly presented one of the three vignettes. Participants answered five items on 1–5 scales. Two items were reverse-coded before the responses were combined into a Nuclear Safety Perception Score.

Each brief bundles arguments with supporting material. Claims about a “long peace” and historical near-misses appear within the treatments for participants to assess. They are not findings produced by the experiment.

The public site records the design and its connection to the Waltz–Sagan debate. It does not publish student response data or characterize the classroom comparison as proof that one narrative induced a particular view.

Takeaways

  1. The security dilemma explains how defensive intentions can generate offensive-looking behavior and reciprocal insecurity.
  2. Deterrence requires survivability and credibility. Communication and organizational control also matter.
  3. Sagan's three models identify distinct routes to acquisition. Complex cases often contain evidence for more than one.
  4. The Waltz–Sagan debate separates the strategic logic of deterrence from the risks of managing arsenals, including organizational failure and accident.
  5. Nonproliferation institutions change information and incentives, but they operate inside the same security environment that motivates acquisition.

Course record checked against the 2025–2026 syllabus and the lecture slides, opening remarks and reading guide. The fielded Qualtrics instrument and analysis workflow were used to verify the classroom study.