THE LONG VIEW

Bottom Line Up Front: The credibility of U.S. extended nuclear deterrence in the Indo-Pacific is eroding, increasing the risk that key allies—particularly South Korea—may pursue indigenous nuclear capabilities within the next decade, undermining global nonproliferation norms and triggering regional arms competition [1,2,8]. Threat Identification: The primary threat is the potential breakdown of the U.S.-led extended deterrence framework, driven by three interrelated factors: (1) advancing nuclear, cyber, space, and biological threats from China, North Korea, and Russia; (2) declining confidence among U.S. allies in Washington’s willingness to use nuclear force in their defense; and (3) growing domestic political and public support for national nuclear options, especially in South Korea [4,12,18]. Secondary threats include the proliferation of non-nuclear strategic weapons (e.g., hypersonic missiles, biological agents) and the possibility of coercive nuclear signaling by China in a Taiwan contingency [6,9]. Probability Assessment: High likelihood of continued erosion in deterrence credibility over the next 3–5 years (2026–2031). Nuclear proliferation by an ally is currently low-probability in the short term due to technical, economic, and diplomatic barriers, but the risk is rising—especially for South Korea, where 70% of the public supports an indigenous nuclear option [18]. If U.S. commitment is perceived as wavering during a crisis (e.g., over Taiwan or the Korean Peninsula), breakout decisions could accelerate rapidly. Japan and Australia remain less likely to pursue nuclear weapons, but both are expanding conventional strike capabilities and deepening strategic dialogues, indicating hedging behavior [13,15]. Impact Analysis: Allied nuclear proliferation would fundamentally destabilize the Indo-Pacific, potentially triggering a cascade of nuclear armament, undermining the Non-Proliferation Treaty (NPT), and fracturing U.S. alliance networks. Even non-nuclear proliferation—such as expanded counterstrike capabilities or nuclear latency—risks miscalculation and escalation. Additionally, failure to reassure allies could lead to strategic decoupling, where partners prioritize autonomy over collective security, weakening deterrence against China and North Korea [3,8]. Recommended Actions: (1) Institutionalize a quadrilateral Extended Deterrence Dialogue (U.S., Japan, South Korea, Australia) to enhance threat and capability sharing; (2) Expand joint nuclear planning and exercises, including tabletop simulations involving non-U.S. allies; (3) Increase U.S. visible deterrence measures (e.g., rotational bomber deployments, sea-launched nuclear cruise missile studies); (4) Launch public and expert education campaigns in allied countries to clarify U.S. nuclear policy and the costs of proliferation; and (5) Strengthen bilateral consultative mechanisms (e.g., U.S.-ROK Nuclear Consultative Group) as models for broader integration [10,11,14]. Confidence Matrix: - Threat Identification: High confidence – Based on official reports, public polling, and documented military developments. - Probability Assessment: Medium-high confidence – Informed by trend analysis and expert assessments, though contingent on future U.S. policy and crisis dynamics. - Impact Analysis: High confidence – Supported by historical precedent and structural alliance theory. - Recommended Actions: Medium confidence – Dependent on political will and intergovernmental cooperation, which vary across capitals [12,16].