Cold War-Level Nuclear Tensions Return to Northeast Asia

As US-Russia relations remain fractured by the Ukraine war, the treaty that has kept their nuclear arsenals in check is about to expire. This represents just one of three converging factors pushing Northeast Asia toward an era of nuclear tension not seen since the Cold War.

The Crumbling Arms Control Architecture

The New START Treaty, which limits both the US and Russia to 1,550 deployed nuclear warheads each, expires in February 2026. With diplomatic channels frozen over Ukraine, neither side has shown interest in renewal talks.

Meanwhile, China's nuclear modernization has shifted into overdrive. The Stockholm International Peace Research Institute reports China's warhead count jumped from 290 in 2019 to 500 in 2024. Pentagon projections suggest China could possess 1,000 warheads by 2030 and 1,500 by 2035 – approaching US and Russian levels.

North Korea adds another layer of complexity. South Korean defense analysts estimate Pyongyang currently holds 50-70 nuclear warheads and can produce 6-18 more annually. Unlike the major powers, North Korea faces no treaty constraints on its nuclear expansion.

The Alliance Dilemma

For US allies in the region, this nuclear buildup creates unprecedented strategic challenges. South Korea and Japan have long relied on American extended deterrence – the promise that US nuclear weapons would protect them. But that guarantee feels less certain as the nuclear landscape shifts.

Donald Trump's return to the presidency adds another variable. During his previous term, he suggested South Korea and Japan might need their own nuclear weapons. Recent polling in South Korea shows 71% public support for indigenous nuclear weapons development – a dramatic shift from previous decades.

Yet the path to nuclear weapons would require South Korea to withdraw from the Nuclear Non-Proliferation Treaty, potentially fracturing its alliance with the US and triggering severe Chinese retaliation. The strategic benefits remain questionable.

The Proliferation Domino Effect

Experts warn of cascading nuclear proliferation across the region. If South Korea goes nuclear, Japan would face enormous pressure to follow suit. This could trigger an even more aggressive Chinese nuclear buildup, creating a four or five-way nuclear competition in Northeast Asia.

Such a scenario would dwarf Cold War complexities, when nuclear competition was largely bilateral between the US and Soviet Union. Managing deterrence relationships among multiple nuclear powers, each with different strategic cultures and risk tolerances, presents unprecedented challenges.

Alternative approaches include nuclear sharing arrangements similar to NATO's model, where US tactical nuclear weapons would be deployed to allied territory under American control. However, this too would likely provoke strong reactions from China and Russia.

Regional Responses and Calculations

China's nuclear expansion appears driven by concerns about US missile defense systems and long-range conventional strike capabilities. Beijing argues it needs a larger, more survivable nuclear force to maintain credible deterrence as US military technology advances.

Russia's nuclear modernization predates the Ukraine war but has accelerated since 2022. Moscow increasingly relies on nuclear threats to offset conventional military weaknesses exposed in Ukraine.

For smaller regional players like South Korea and Japan, the calculation is different. They must balance the security benefits of nuclear weapons against the diplomatic costs and the risk of triggering a regional arms race that ultimately leaves them less secure.