Same Pressure, Different Responses Leader Perceptions and the Non-Linear Evolution of Japan’s Security Policy, 2011–2025

Structural realism predicts that a state facing a deteriorating balance of power should respond with proportional, linear military buildup and balancing. Previous studies on Japan’s security policy over the past decade and a half have mostly interpreted this trajectory as an evolutionary shift toward balancing. This paper argues, however, that Japan’s trajectory has instead been markedly non-linear: successive governments have oscillated between alliance restoration, dual-track engagement-and-balancing, and, most recently, a paradigm shift toward “fundamental deterrence.” This paper draws on the Perceptual Neoclassical Realist (PNCR) framework to argue that this non-linearity is best explained not by variation in the level of structural pressure itself, but by how successive Japanese leaders have perceived that pressure. Treating leader perception as the crucial transmission belt between systemic stimuli and policy output, the paper traces how the independent variable, specifically the intensifying structural pressure from China’s rise and the erosion of US-led unipolarity, has been filtered through leaders’ threat assessments, judgments of alliance credibility, and readings of domestic political constraint, to produce the dependent variable: a foreign and security policy that has evolved in fits and starts rather than smoothly. The argument is developed through three sequential case studies spanning four administrations. First, the Noda government (2011–2012) met the initial reversal in the Sino-Japanese power balance with a cautious return to the US alliance, constrained by disillusionment with earlier liberal-regionalist ambitions and a fragile domestic base. Second, the second Abe government (2012–2020) confronted intensifying pressure from an assertive China and an increasingly transactional United States with the more complex “dual-track” approach of Proactive Pacifism, which centered on collective self-defense and the Free and Open Indo-Pacific vision supplied the balancing track, while a parallel effort to stabilize and engage Beijing supplied the engagement track. This dual-track approach was underpinned by a dual threat perception that sought to “shape” rather than exclude China, and by Abe’s confidence in his own summit diplomacy to manage Washington. Third, the Kishida and Ishiba governments (2021–2025) produced the sharpest shift of the three cases: counterstrike capability, expanded defense spending, and denser minilateral security networks. This might seem to simply track intensifying structural pressure. Yet neither leader’s profile predicts it: Kishida had long been seen as dovish, Ishiba was not conventionally regarded as a hardliner either. Their convergence, the paper argues, reflects not ideology but a shared perceptual rupture. Russia’s invasion of Ukraine and sharpening US-China rivalry shattered assumptions of a “manageable” East Asia, eroding confidence in alliance credibility, overriding prior dispositions, and precipitating the shift toward fundamental reinforcement of deterrence and response capabilities. By comparing four leaders who share a broadly realist, conservative orientation yet diverge sharply in how they perceived threat urgency, alliance reliability, and domestic constraint, the paper demonstrates that perception, rather than structural pressure alone, drives the variation in Japan’s foreign policy responses.