U.S. extended deterrence in the Asia Pacific has historically aimed not only to deter U.S. adversaries, such as China and the DPRK, from engaging in conventional or nuclear attacks on U.S. regional allies, but also to disincentivize allies from acquiring an independent nuclear capability. The potential for allied nuclear armament has recently made headlines, with prominent politicians in the region raising questions about the continued credibility of the U.S. nuclear umbrella and, in some cases, openly endorsing the need for an indigenous nuclear weapons program.
How the U.S. should interpret and respond to these challenges was a topic of discussion at the April 2025 “Strengthening Deterrence in the Indo-Pacific” workshop, facilitated by the Center for Global Security Research at Lawrence Livermore National Laboratory (LLNL). This essay analyzes the potential for allied armament in South Korea and Japan, including drivers of regional proliferation, the current state of public and elite opinion in both countries, and how the United States should respond. While this paper draws on insights from the recent LLNL workshop, the opinions presented are the author’s own and do not represent any organization.
The Regional Deterrence Architecture and Drivers of Proliferation
The U.S. deterrence architecture in the Asia Pacific is focused on bilateral partnerships with key allies – principally, Australia, Japan, and South Korea. Maintaining a forward U.S. presence is necessary to signal a robust commitment to allies, force adversaries to engage the U.S. early in conflict, and deny adversaries an outright advantage. The existing deterrence architecture is designed to convince adversaries, including China, the DPRK, and Russia, that violence against allies will incur costs that exceed benefits and risk greater war.
Increasingly, this architecture has come under strain. Gaps in the regional deterrence architecture, along with advances in adversaries’ conventional and nuclear capabilities, threaten the credibility of the U.S. extended deterrent and may, in turn, increase allies’ incentives to proliferate. The United States must now contend with the possibility of conflict with two nuclear peers, China and Russia, with China expected to reach nuclear parity with the U.S. by 2035. The possibility of simultaneous engagement extends to the DPRK, which may initiate a crisis on the Korean Peninsula as a distraction or leverage an ongoing regional conflict to pursue its territorial aims. The increasing political-military alignment between Russia and China, as well as Russia and the DPRK, makes this problem more urgent.
Additionally, the U.S. nuclear foundation faces external stress due to an increase in targets that must be held at risk, including hardened and mobile targets, and the “tyranny of distance” in deploying nuclear weapons from the U.S. to the region. The foundation is also under internal stress as the entire strategic force undergoes modernization, including nuclear command and control. These stressors may impact allied perceptions of U.S. political and technical credibility, including whether the U.S. will be able to successfully complete its modernization program and deliver all necessary capabilities.
Recent U.S. policy positions have also elicited concern from regional allies. Washington has pressured its regional allies to take on more of the burden for their defense, including linking defense cost-sharing to broader trade disputes. The Trump administration has previously floated the potential of removing U.S. troops from the region if cost-sharing expectations are not met. Additionally, shifting positions on the U.S. approach to the DPRK have raised alarm with South Korean policymakers. Both President Trump and Secretary of Defense Pete Hegseth have publicly referred to North Korea as a “nuclear power,” potentially legitimizing the DPRK’s nuclear weapons status. At his confirmation hearing, U.S. Undersecretary of Defense for Policy Elbridge Colby further emphasized the need to restructure U.S. Forces Korea to focus primarily on threats posed by China rather than the DPRK.
As with U.S. NATO allies, allies in the Asia Pacific are likely to tolerate and, in some cases, embrace moderate pressure from the United States to increase defense spending and burden sharing. However, stronger signals of U.S. abandonment, such as the removal of U.S. troops from the Korean peninsula or U.S. abandonment of Taiwan, are likely to incentivize allied proliferation.
Public Opinion Towards Nuclear Armament in South Korea and Japan
The South Korean public has long supported acquiring nuclear weapons, with upwards of 75% of the population expressing support in recent opinion polls. Elite opinion has historically been more divided; however, polling indicates that South Korean political elites could change their position on nuclear weapons in response to U.S. signals of abandonment, such as troop withdrawals. Recent South Korean debate about developing its nuclear capability likely reflects that South Korea is no longer willing to take the U.S. extended deterrence commitment at face value – it wants to be more actively involved in its defense and requires more information to feel assured.
In contrast to South Korea, the Japanese public remains firmly opposed to acquiring nuclear weapons. Recent polls suggest that more than 70% of the populace believes Japan should promote global nuclear disarmament, with similar numbers in support of Japan signing onto the Treaty on the Prohibition of Nuclear Weapons. Despite an overwhelmingly unified public, prominent Japanese politicians have publicly advocated a different approach. Most notably, in 2024, Prime Minister Ishiba called for nuclear sharing with the United States through the creation of an “Asian NATO.”
In the event that South Korea moves forward with developing an independent nuclear capability, Japan may also be more likely to nuclearize. At minimum, this scenario would likely result in contentious political debate in Japan. Ultimately, however, the current threshold for acquiring nuclear weapons in Japan is very high. It is thus important to consider South Korea and Japan independently rather than treat the region as a monolith.
Conclusion: Next Steps for the United States
As debate over the credibility of the U.S. extended deterrent continues, some U.S. and South Korean academics and political commentators have suggested that the United States should allow its Asian allies to acquire nuclear weapons. Other proposals from the academic and policy community include the pursuit of nuclear latency or a nuclear sharing agreement with the United States. The U.S. must critically evaluate these proposals and determine whether preventing allied proliferation in the Indo-Pacific should remain a primary goal of the regional deterrence architecture. If so, reassurance of allies will be key.
Reassuring allies will require thoughtful consideration of how to address the drivers of regional proliferation, from gaps in the regional deterrence architecture to policy positions that weaken allied confidence in the U.S. commitment. As allies seek to become more involved in their defense, including pursuing greater operational autonomy and strategic input, the United States can build upon existing regional deterrence dialogues to enhance transparency, expand information sharing, and integrate allies more fully into strategic planning. The United States may also need to reevaluate its budgetary priorities, including whether to augment theater nuclear forces to address regional security shortfalls and mitigate allied concerns about U.S. capacity and will.
Noelle J. Camp is a Nonresident Fellow and the Lead of East Asia and Pacific programming for the Cooperative Monitoring Center (CMC) at Sandia National Laboratories. She advises government and industry clients on topics including nonproliferation, nuclear and radiological security, and export controls as a consultant with Camp Research & Consulting, LLC.
Photo: Defense Secretary Pete Hegseth and Japanese Defense Minister Gen Nakatani hold a joint press briefing at the Japanese Ministry of Defense in Tokyo, March 30, 2025. Source: Air Force Senior Airman Madelyn Keech, DOD
