Under What Conditions Might South Korea Go Nuclear? Alliance Credibility, Domestic Pressures, and the Limits of Extended Deterrence

Abstract

Extended deterrence has long enabled U.S. allies to forgo nuclear weapons while remaining secure under the American nuclear umbrella. As adversaries acquire the ability to threaten the U.S. homeland and alliance politics grow more volatile, the credibility of these guarantees has come under increasing strain. This article examines the conditions under which a non- nuclear U.S. ally may move toward nuclear acquisition, using South Korea between 2022 and 2025 as a critical case. It evaluates two competing, though not mutually exclusive, mechanisms shaping nuclear decision-making: alliance credibility and domestic political pressures. Drawing on public opinion data, elite political discourse, alliance behavior, and regional security developments, the article finds that while both mechanisms have intensified, neither has yet produced an irreversible shift toward nuclear prolifer- ation. Instead, South Korea has adopted a strategy of nuclear hedging, expanding nuclear-adjacent capabilities while remaining formally committed to the Non-Proliferation Treaty. The findings suggest that nuclear restraint within the U.S.-led order remains resilient but conditional, dependent on sustained alliance reassurance and domestic restraint. More broadly, the South Korean case highlights the fragility of nonproliferation under conditions of strategic uncertainty.