Towards South Korean Nuclear Weapons? Political and Strategic Considerations

Key Chapter Title List

1. Current State of the Seoul Debate
2. Peninsula Power Dynamics
3. U.S. Extended Deterrence and the Trump Second-Term Administration
4. Obstacles to Developing an Indigenous Nuclear Program
5. Conclusion

Document Introduction

This report, published by the French Foundation for Strategic Research (FRS) in January 2025, aims to delve into the possibility of South Korea seeking to develop an autonomous nuclear weapons capability and the associated political and strategic complexities. Using South Korean President Yoon Suk Yeol's January 2023 remarks about considering nuclear acquisition as a starting point, the report notes that as North Korea's nuclear and missile capabilities continue to advance, and with the uncertainty brought by former U.S. President Donald Trump's re-election in November 2024, the domestic debate in South Korea over whether it should possess its own nuclear deterrent is entering a new phase.

The report first analyzes the current state of the domestic debate in South Korea. The study points out that although public opinion has long shown 60-70% of respondents supporting South Korea's development of nuclear weapons, with this support being particularly strong among conservative People Power Party (PPP) voters, the current discussion is more of a "noise," filled with politically motivated statements rather than in-depth analysis of the strategic pros and cons of the options. Notably, public support for nuclear armament does not primarily stem from distrust in U.S. extended deterrence but is more based on a strategic calculation that only South Korea itself possessing nuclear weapons can restore strategic balance on the peninsula and deter North Korea.

Secondly, the report assesses North Korea's military capabilities, particularly the fundamental changes its rapid development of nuclear and missile capabilities has brought to the peninsula's power balance. By developing multiple Intercontinental Ballistic Missile (ICBM) models, including those using solid propellant, North Korea has significantly enhanced the credibility and survivability of its second-strike capability. Simultaneously, its vast arsenal of short-range missiles increases the vulnerability of South Korea's critical infrastructure. In response, South Korea has developed and integrated a "three-axis" deterrence strategy consisting of "preemptive strike," "massive punishment and retaliation," and "missile defense," but still believes conventional deterrence alone is insufficient against a nuclear-armed adversary.

The third section focuses on the credibility of U.S. extended deterrence, particularly the potential impact of a Trump second term. While the Biden administration attempted to strengthen security commitments to South Korea through measures like the April 2023 Washington Declaration, Trump's return introduces new uncertainties. The report notes that Trump's past transactional approach demanding allies bear more defense costs, his preference for direct engagement with North Korea, and the threat of potentially reducing U.S. troops in South Korea have all weakened Seoul's confidence in U.S. commitments. However, the report also mentions that some Republican advisors might push for a stronger deterrence posture in the Indo-Pacific, and even Trump himself, motivated by considerations like reducing U.S. costs, might have a degree of potential tolerance for a South Korean nuclear program.

Finally, the report details the numerous obstacles South Korea would face in developing its own nuclear program. Withdrawing from the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) and developing a military nuclear program would most likely lead to a rupture in the alliance with the United States and trigger automatic sanctions under relevant U.S. domestic laws (such as the 1978 Nuclear Non-Proliferation Act). Even with U.S. acquiescence, South Korea would face broad international sanctions, dealing a severe blow to its deeply integrated global economy and encountering significant technical difficulties in areas like nuclear fuel supply. Although the public seems to underestimate the consequences of sanctions, South Korea's elite are likely well aware of the immense costs nuclear armament would entail.

The report's conclusion emphasizes that against the backdrop of North Korea's ongoing nuclear arsenal modernization and increasing U.S. policy uncertainty, domestic calls in South Korea for developing nuclear capabilities may intensify. However, any such policy shift requires a comprehensive weighing of its strategic impact, consequences for inter-Korean relations, changes in relations with other regional countries, shocks to the alliance system, and severe economic and technological costs. A South Korean withdrawal from the NPT would also cause lasting damage to the already stressed global nuclear non-proliferation norm. Based on a comprehensive review of public policy statements, academic research, opinion polls, and expert analysis, this report provides a professional and balanced assessment framework for understanding this highly complex strategic issue.