Cold War-level nuclear tensions return to Northeast Asia

With US-Russia relations already badly damaged by the Ukraine war, the treaty that has restrained the number of US and Russian nuclear warheads is about to expire. That is only one of three factors pushing Northeast Asia toward an era of heightened nuclear tension.

One result may be a new round of proliferation in the region, which has been rare to date, with only two countries — China in 1964 and North Korea in 2006 — joining the nuclear club over the past 77 years.

During the Cold War, Russia possessed as many as 45,000 nuclear warheads, while the United States had up to 31,000.

Eventually, the two superpowers agreed to negotiate limits. This culminated in the New START Treaty — an acronym for Strategic Arms Reduction Talks — which has been in effect since 2011. The treaty limits the US and Russia to deploying a maximum of 1,550 nuclear warheads each. It also caps the number of deployed delivery vehicles and heavy bombers.

New START, however, is collapsing. It has been shaky since 2023, when, due to the Ukraine war, both countries stopped allowing the outside inspections of nuclear facilities required by the treaty. A definitive end is now on the horizon, as the treaty is scheduled to expire on February 5.

New START ending

Moscow has proposed extending the numerical limits on weapons systems in New START for one year beyond the expiration date. The Russian government says the US side has not responded to the proposal. In January, the US president said, “If it expires, it expires. We’ll just do a better agreement.”

Producing a new and better agreement may not be so simple. Arms control experts doubt that an agreement superior to New START is possible. They also argue that it would be unwise to let New START expire with nothing prepared to replace it. For an indefinite period, there would be no restraints on strategic arms racing between Russia and the US.

Several negative consequences could follow. The two countries might again greatly expand their nuclear arsenals. This would be a major setback to the global elimination of nuclear weapons, a stated goal of both the Donald Trump and Vladimir Putin governments.

Through inspections, arms control agreements provide each side with regularly updated information about the other. Absent such information, both sides are prone to making worst-case assumptions, which can lead to miscalculations that increase the risk of conflict.

Ideally, the two countries should not only maintain their existing limits on legacy nuclear weapons systems but also expand negotiations to include exotic new systems such as hypersonic glide vehicles, nuclear-powered cruise missiles and nuclear-armed underwater drones — all of which Russia has tested. These potentially destabilizing technologies remain outside international regulation.

Chinese aloofness

The end of the US-Russia agreement suggests an opportunity to expand talks to include the world’s third-largest nuclear power. China is in the midst of a dramatic buildup of its nuclear forces, from fewer than 300 warheads in 2020 to an expected 1,000 — deployed and non-deployed — by 2030. Even at that level, current US and Russian arsenals, at 5,177 and 5,459 warheads respectively, would still dwarf China’s.

Beijing is therefore unlikely to join a tripartite agreement anytime soon. Reduce your arsenals to our level and then we will talk, Chinese officials have said for decades. Retired PLA Senior Colonel Zhou Bo, an international affairs commentator, has called the idea of the US and Russia imposing arms control on China “ridiculous,” comparing it to an obese man inviting a thin man to follow the same weight-loss program.

China’s strategic thinking is influenced by recent history. Both superpowers made nuclear threats against China during the 1950s and 1960s, and both also attempted to slow or block China’s own nuclear weapons development.

Chinese planners lack confidence in the durability of China’s second-strike capability, given what they see as continuing US efforts to undermine it. The US is upgrading its silo-based nuclear missiles — which are more than 50 years old — at great expense, and the US president has touted a “Golden Dome” system that would reliably intercept incoming enemy missiles.

At least in the medium term, China is likely to remain in force development mode, setting aside reassurance and risk reduction.

Shifting US attitude

A second factor raising nuclear tensions in Northeast Asia is a shift in Washington’s attitude. Until recently, the US government opposed nuclear proliferation with near-religious zeal, a commitment that was bipartisan.

President Ronald Reagan, a Republican, said in 1981 that the US would “seek to prevent the spread of nuclear explosives to additional countries as a fundamental national security and foreign policy objective.” President Barack Obama, a Democrat, said in 2009, “The world must stand together to prevent the spread of these weapons.”

Until now, there has been an understanding among Washington and its allies Japan and South Korea that all three would continue to insist on “the complete denuclearization” of North Korea (DPRK) — a phrase reiterated, for example, in three separate meetings in 2025 among the three countries’ foreign ministers.

As part of this understanding, the US government has refused to accept the DPRK as a “nuclear weapons state,” a legal term under the Nuclear Nonproliferation Treaty that implies international acquiescence to a country’s possession of nuclear arms. The current US government, however, appears less committed to this policy. Trump has on multiple occasions publicly referred to North Korea as a “nuclear power.”

In a 2016 interview with CNN, Trump said, “At some point we have to say … we’re better off” if Japan and South Korea acquire nuclear weapons. Similarly, Undersecretary of Defense for Policy Elbridge Colby, a leading strategist in the administration, has said he believes that South Korea may need its own nuclear weapons and that US policy toward North Korea should shift from denuclearization to arms control.

Washington is now considering inviting North Korea to participate in arms control talks. In an interview with The New York Times on January 11, Trump spoke of seeking a new agreement with Russia and China. He said “it would be desirable to bring in a couple of other players.” He declined to name them, but one would presumably be the DPRK.

Washington has long vowed that “the United States does not, and never will, accept North Korea as a nuclear state.” Analysts have long argued that doing so would seriously damage the global nonproliferation regime. It would also fuel the third factor contributing to rising nuclear tensions in Northeast Asia.

Japan and South Korea feel unsafe

Both South Korea and Japan are increasingly inclined to believe they need their own nuclear weapons, and for similar reasons: Their adversaries are growing stronger and more hostile, and they doubt the reliability of US protection.

Both countries possess the technological capability to deploy nuclear weapons relatively quickly if they choose. A nuclear breakout is not imminent in either case, but the forces pushing in that direction appear robust.

In the Republic of Korea (ROK), a majority of the public has favored acquiring nuclear weapons for several years. The Biden administration bought some time with the 2023 Washington Declaration, which reaffirmed the US commitment to retaliate with American nuclear weapons in response to any North Korean nuclear attack against the South. Trust in US protection has declined, however, since Trump returned to the White House.

The second Trump administration’s National Defense Strategy (NDS), released on January 23, foresees handing South Korea “primary responsibility for deterring North Korea with critical but more limited US support.” While the US remains willing to maintain the nuclear umbrella, it may now move toward withdrawing US troops stationed in the ROK.

Colby, currently visiting South Korea, is likely to raise this issue. The NDS also re-emphasizes the US demand that allies raise defense spending to 5% of GDP, a politically difficult goal for both South Korea and Japan. All of this reinforces South Koreans’ sense that the US commitment to their defense is waning.

South Korea depends on foreign suppliers for enriched uranium to fuel the nuclear power plants that provide one-third of its electricity. Under the Nuclear Nonproliferation Treaty and Nuclear Suppliers Group rules, that supply is contingent on South Korea not developing nuclear weapons.

Under the current rules, seeking nuclear arms would devastate the country’s economy. It is possible, however, that these rules could weaken as US interest in supporting international institutions declines or as Washington pressures partners to carve out an exemption for South Korea.

Since 1967, Japanese government policy has been based on three principles: not possessing, not producing and not permitting the introduction of nuclear weapons. The latter refers to the possibility of basing US nuclear weapons in Japan.

Japanese Prime Minister Sanae Takaichi, however, has ordered a review of the policy. An unnamed senior official in her government caused a stir in December by saying, “I think we should possess nuclear weapons.” The idea has shifted from unthinkable to controversial.

A strong nuclear taboo persists among the Japanese public, which remains mostly opposed to acquiring nuclear weapons. A significant part of that opposition would likely disappear, however, if South Korea went nuclear. In any case, history cautions against underestimating a state’s willingness to take drastic — and unpopular — steps when it believes its survival is threatened.

Both South Korea and Japan plan to build nuclear-powered — but conventionally armed — submarines. These vessels may provide a back door to nuclear weapons development, as their engines run on enriched uranium.

To operate such submarines independently, both countries would need to expand facilities for uranium enrichment and spent-fuel reprocessing. Enriched uranium can also be used as fuel in nuclear weapons. This did not deter Washington from agreeing in 2025 to help South Korea build nuclear-powered submarines.

A nuclear Taiwan?

Taiwan is another, if less likely, candidate for proliferation. Like Japan and South Korea, Taiwan has the technical capability to build nuclear weapons. From the 1960s through the 1980s, Taiwan’s government attempted to start a nuclear weapons development program but ultimately abandoned it due to consistent US opposition.

Many analysts argue that attempting to acquire nuclear weapons would make Taiwan less rather than more secure. There is, nevertheless, a logical rationale for a state that is hopelessly outmatched by a potential aggressor’s nuclear and conventional forces to seek a small nuclear arsenal as a deterrent.

Despite China being able to completely destroy Taiwan, the prospect of losing Beijing and Shanghai in return for control over an irradiated wasteland would compel the Chinese government to think more carefully about a forcible annexation of the island.

Taiwan’s current government professes no interest in nuclear weapons, but the combination of Japan and South Korea going nuclear, declining confidence in US military support and a worsening threat from China could revive Taiwan’s desire to acquire its own nukes.

A defining feature of the Cold War, nuclear tensions may soon become more prominent in the new cold war as well. The near future could see renewed and unrestricted nuclear arms racing between the US and Russia, the emergence of at least two new nuclear weapons states in Northeast Asia and the continued rapid expansion of China’s arsenal.

While countries may seek security by reinvesting in nuclear weapons, this trend also reflects deepening distrust and pessimism while sharply raising the potential lethality of conflicts.

Denny Roy is a senior research fellow at the East-West Center, Honolulu.