How much risk is there of a nuclear cascade in Northeast Asia?

This paper assesses the risk of a “nuclear cascade” in Northeast Asia, arguing that proliferation pressures are more likely to unfold as a gradual, political erosion of constraints than as a rapid domino-style reaction. It conceptualizes cascades as sequences in which governments progressively lower barriers to a nuclear option—through public debate, legal reinterpretation, fuel cycle choices, and institutional preparation—until maintaining non-nuclear restraint becomes harder than crossing the threshold. The analysis develops a three-step causal pathway: (1) North Korea leverages its mature nuclear deterrent and expanding missile capabilities to coerce and strain U.S. alliances; (2) China’s accelerating nuclear modernization and growing arsenal intensify regional “decoupling” anxieties by raising perceived risks and costs of U.S. intervention; and (3) these pressures, filtered through perceptions of U.S. extended-deterrence credibility, push Japan—and, by extension, South Korea—toward deeper “threshold capability,” even if overt weaponization remains politically contested. The paper highlights how technical latency (including sensitive fuel cycle features and plutonium management), alliance reassurance mechanisms, and shifting domestic discourse interact to shape nuclear decision pathways. It concludes that cascade risk is real but not deterministic, and that effective prevention hinges on strengthening allied consultation and crisis-management, sustaining credible conventional deterrence, maintaining transparency and stockpile-reduction practices, and expanding risk-reduction and arms-control measures to dampen misperception and escalation dynamics.