A Festival of Nuclear Umbrellas: Extended Nuclear Deterrence with Asian Characteristics

The broader securitization of global and regional developments during the current decade is evident not only in Europe and the Middle East, but also across the Asia-Pacific. The growing salience of security concerns has unfolded against the backdrop of intensifying U.S.–China strategic rivalry and is, to a significant extent, driven by it. In particular, the increasing importance of the nuclear factor in its broadest sense merits attention. As turbulence in the international system continues to grow, robust security guarantees are becoming ever more valuable, enabling states to reduce the likelihood of external military intervention.

Possessing nuclear weapons is hardly the only way to guarantee a country’s security and sovereignty. However, given the constraints imposed by the non-proliferation regime, the substantial financial and reputational costs associated with acquiring nuclear weapons, and a range of other factors, not all states are capable of securing their national interests through indigenous nuclear capabilities. To date, only ten of the UN's 193 member states have successfully developed military nuclear programs, while South Africa remains the only country in history to have voluntarily relinquished its nuclear arsenal. Extended nuclear deterrence offers a means of circumventing these constraints by effectively delegating responsibility for territorial defense to a more capable partner possessing nuclear weapons and the means to deliver them. Dozens of U.S. allies around the world have thus come to rely on collective defense arrangements—most notably in their multilateral form in Europe—and on bilateral security commitments, as in Asia.

Extended nuclear deterrence as applied to U.S. allies in Asia is far from a monolithic phenomenon. On the contrary, such guarantees are clearly heterogeneous: ranging from sporadic verbal assurances in the case of Taiwan to de facto joint nuclear planning with the Republic of Korea. Moreover, the level of guarantees extended to individual actors has varied significantly over time. The overt deployment of nuclear weapons and delivery systems on allied territory may give way to a guarantor's relative disengagement from the beneficiary's security concerns—a dynamic that is increasingly evident today. This phenomenon may be described as a “festival of nuclear umbrellas,” by analogy with the notion of a “patchwork quilt,” a term commonly used to characterize both the broader U.S. alliance architecture in the Asia-Pacific and the multiplicity of economic initiatives across the region.

Extended nuclear deterrence is, to a large extent, a conceptual construct whose effectiveness depends on a multitude of variables. Despite the absence of explicit references to the nuclear option in the numerous bilateral and minilateral agreements between the United States and its allies, prevailing interpretations of these arrangements tend to take extended nuclear deterrence as a given. This has led both to the institutionalization of various joint formats—from military exercises to nuclear planning groups, or at least coordination frameworks—and to the doctrinal entrenchment of the concept in the strategic documents of the United States and its allies. At the same time, fluctuations in the implementation of this form of deterrence only reinforce the argument that perceptions and threat assessments on the part of both the guarantor and the beneficiaries are of critical importance. Unlike NATO arrangements, the Asia-Pacific has not seen the deployment of nuclear weapons on allied territory since 1991. A change in this approach remains unlikely in the short term, even amid the voluntarist policies pursued by the Trump administration. Moreover, whereas in Europe priority is given to the air leg of the U.S. nuclear triad—namely gravity bombs deliverable by dual-capable aircraft—in the Asia-Pacific greater significance attaches to the submarine component. This can be seen in such examples as AUKUS and visits by U.S. nuclear-powered submarines to South Korean ports.

At the same time, the European and Asian theatres exhibit an important similarity: in recent decades, the credibility dilemma surrounding U.S. security guarantees has become particularly acute. In Charles de Gaulle’s classic formulation, it is encapsulated in the question of whether Washington would be willing to “trade New York for Paris” in the event of a nuclear exchange. For America’s key partners in the Asia-Pacific, this logic remains equally relevant—it is enough simply to replace Paris with Tokyo, Seoul, Canberra, or Taipei. It is during Donald Trump’s second term that distrust of U.S. security guarantees has become even more pronounced, even if not necessarily expressed openly. This stems both from the broader instability of the international environment and from the unpredictability of the guarantor itself, manifested in the current Republican administration’s at times seemingly irrational foreign policy decisions.

In this regard, despite the additional guarantees formalized under Joe Biden, it is possible to anticipate a further erosion of the extended nuclear deterrence system in the Asia-Pacific, albeit not as pronounced as in Europe. U.S. allies may increasingly take steps toward providing for their own security, though for now these efforts remain cautious and tentative. In the medium term, however, particularly if the strategic environment continues to deteriorate, the beneficiaries of U.S. security guarantees may begin to pursue more systematic measures to strengthen their own security—whether unilaterally or through bilateral and multilateral arrangements, including in minilateral formats.

The broader securitization of global and regional developments during the current decade is evident not only in Europe and the Middle East, but also across the Asia-Pacific. The growing salience of security concerns has unfolded against the backdrop of intensifying U.S.-China strategic rivalry and is, to a significant extent, driven by it. In particular, the increasing importance of the nuclear factor in its broadest sense merits attention. As turbulence in the international system continues to grow, robust security guarantees are becoming ever more valuable, enabling states to reduce the likelihood of external military intervention.

Possessing nuclear weapons is hardly the only way to guarantee a country’s security and sovereignty. However, given the constraints imposed by the non-proliferation regime, the substantial financial and reputational costs associated with acquiring nuclear weapons, and a range of other factors, not all states are capable of securing their national interests through indigenous nuclear capabilities. To date, only ten of the UN's 193 member states have successfully developed military nuclear programs, while South Africa remains the only country in history to have voluntarily relinquished its nuclear arsenal. Extended nuclear deterrence offers a means of circumventing these constraints by effectively delegating responsibility for territorial defense to a more capable partner possessing nuclear weapons and the means to deliver them. Dozens of U.S. allies around the world have thus come to rely on collective defense arrangements—most notably in their multilateral form in Europe—and on bilateral security commitments, as in Asia.

Gleb Toropchin:
A Monsoon Instead of a Gentle Breeze: Creeping Nuclearization in the Asia-Pacific

A Terminological Excursus

Nuclear non-proliferation and arms control are subfields of international security studies characterized by dense and highly specialized terminology. Often, such concepts have similar but distinct meanings.

The core concept for the purposes of this discussion is extended nuclear deterrence—a set of arrangements and measures through which a nuclear-weapon state and its ally (or allies) seek to deter a common potential adversary. It should be distinguished from positive security assurances, which are best understood as commitments to assist a non-nuclear-weapon state that has come under attack. Negative security assurances, in turn, refer to commitments by nuclear-weapon states not to use nuclear weapons against non-nuclear-weapon states.

“Nuclear umbrella” is a common term used in everyday language to refer to commitments regarding extended nuclear deterrence. This ubiquitous journalistic cliché has become a “dead metaphor” that actively finds its way into academic writing as well. From a structural perspective, it is important to recognize the inherent asymmetry of extended nuclear deterrence: a nuclear-armed guarantor provides security for a beneficiary, thereby reinforcing the latter’s lack of nuclear weapons. Moreover, some scholars argue that extended nuclear deterrence—and even the deployment of nuclear weapons on the territory of non-nuclear-weapon states—serves to strengthen the international nuclear non-proliferation regime by reducing the beneficiary’s incentive to acquire nuclear weapons of its own.

Extended Nuclear Deterrence: Global Practice

The first model of extended nuclear deterrence is embodied in NATO. The alliance’s well-known Article V is based on the principle that “an attack against one member is considered an attack against all.” The article’s scope is geographically limited to Europe and North America. The European model is characterized by so-called nuclear-sharing arrangements (sometimes referred to as the joint use of nuclear weapons). These involve the possibility of transferring control over nuclear weapons to NATO’s European members, as well as their participation in joint nuclear planning and exercises. U.S. B61-12 gravity bombs, the latest modification of the B61 family, are currently deployed at bases in five NATO countries in Europe: Belgium, Germany, Italy, the Netherlands, and Turkey. Since Donald Trump’s return to the White House, discussion has intensified regarding the possibility of creating an intra-European deterrent. France has emerged as the most prominent actor in this debate, signing the Northwood Declaration with the United Kingdom in July 2025 and putting forward the concept of “forward deterrence” in March 2026.

Increasing attention is also being paid to the deployment of the Oreshnik missile system in the Republic of Belarus, which could potentially serve as a delivery vehicle for nuclear weapons. Recent joint exercises conducted by Russian and Belarusian forces may appear, at least morphologically, comparable to NATO’s nuclear-sharing arrangements. More broadly, Russia’s current nuclear doctrine, set out in the document “Fundamentals of State Policy of the Russian Federation on Nuclear Deterrence” of 19 November 2024, provides for the possible use of the nuclear option by Moscow in response to an attack not only against Russia itself, but also against its allies. Shortly after the document’s adoption, Secretary of the Security Council of the Russian Federation Sergei Shoigu confirmed that Russia’s “nuclear umbrella” extends to the other members of the Collective Security Treaty Organization.

The characteristics of extended nuclear deterrence in the Asian context are shaped by the historical and legal nuances of the relationship between the United States and its allies in the Asia-Pacific region. Since the Cold War, the region’s alliance system has resembled a “hub-and-spokes” model, with Washington building its network of defense treaties primarily on a bilateral—and more rarely trilateral—basis. Throughout the second half of the twentieth century, U.S. tactical nuclear weapons (TNW) and their delivery systems were deployed on the territory of American allies in Asia. It was only with the end of the Cold War that these weapons were withdrawn from the region.

Current shifts in the architecture of the international environment are driving changes in the region’s military-political configuration. The traditional “hub-and-spoke” model is increasingly being supplanted by a networked architecture, as U.S. allies and partners conclude defense agreements among themselves without Washington’s direct involvement. These processes began under Joe Biden, and the foreign policy course of the current U.S. administration, operating under the banner of “America First,” may provide an additional impetus for the development of intra-regional ties. Notably, the Department of Defense under Pete Hegseth has deliberately refrained from regularly updating the Nuclear Posture Review, a document that has traditionally served as a vehicle for reaffirming U.S. commitments to the defense of its allies. The current version was published by the previous administration in 2022; the term “extended deterrence” alone appears in it more than a dozen times. Against this backdrop, the current administration’s explicit refusal to use the term “extended nuclear deterrence” in the 2026 National Defense Strategy is no less noteworthy. These trends further underscore the distinctive ways in which the concept of extended nuclear deterrence is being implemented with respect to U.S. Asian allies and partners.

The Republic of Korea: A Swinging Pendulum

The Republic of Korea became part of the U.S. extended nuclear deterrence framework following the end of the Korean War. Article II of the 1953 Mutual Defense Treaty provides for Washington and Seoul to jointly develop measures for deterring threats, while Article III defines the Pacific region as the geographical scope of the agreement. Despite Paragraph 13(d) of the Korean Armistice Agreement, which prohibited the parties from deploying new types of weapons, the United States unilaterally declared itself no longer bound by such obligations. U.S. tactical nuclear weapons remained deployed in the Republic of Korea longer than anywhere else in the region—from 1958 to 1991.

With the collapse of the bipolar system, however, Seoul remained under the U.S. “nuclear umbrella.” In 2006, the United States formally declared that extended nuclear deterrence guarantees would apply to the Republic of Korea. A bilateral consultative mechanism was established in 2010, followed in 2016 by the creation of the Extended Deterrence Strategy and Consultation Group. A key milestone was the signing of the Washington Declaration by Yoon Suk Yeol and Joe Biden in April 2023. The declaration specifically provided for the possible deployment of U.S. strategic assets to the Republic of Korea; a commitment reflected in the increased frequency of visits by U.S. submarines—potentially carrying nuclear-armed missiles—to South Korean ports. The establishment of the Nuclear Consultative Group marked a further stage in the institutionalization of joint nuclear planning.

Recent history suggests that the regular alternation of center-left and conservative governments—a process resembling a swinging pendulum—has not undermined Seoul's commitment to its alliance with the United States. The accession to power of the moderate nationalist administration led by Lee Jae-myung following Yoon Suk Yeol's unsuccessful attempt to impose martial law in December 2024 has proven no exception. That said, enthusiasm for the trilateral framework involving the United States and Japan appears to have somewhat diminished.

The factor most likely to affect South Korea's trust in Washington is not so much the domestic political landscape as the actions of the United States itself. Donald Trump's demands that Seoul "pay for its security"—that is, for the stationing of a U.S. military contingent of approximately 25,000 personnel—were first voiced during his first term in office (and even during his first presidential campaign). Such moves do little to bolster the beneficiary's confidence in the guarantor's willingness to come to its defense in the event of a conflict. This is particularly true against the backdrop of reports that amendments to the DPRK Constitution provide for the use of the nuclear option in the event of the elimination of North Korea's leadership in a so-called "decapitation strike."

Alexander Yermakov:
Life After New START: Three Questions for the World

Japan: A Cure for Nuclear Allergy?

The foundations of U.S.-Japanese defense cooperation were originally laid by the 1951 San Francisco Peace Treaty and the subsequent 1952 Security Treaty. In 1960, the latter was replaced by the Treaty of Mutual Cooperation and Security (the U.S.-Japan Security Treaty). Article V stipulates that an external attack on Japan may serve as grounds for U.S. intervention, while Article VI provides for the deployment of military bases on Japanese territory. An accompanying secret agreement authorized the presence of U.S. aircraft and naval vessels—including those capable of carrying nuclear weapons—in Japan's airspace and territorial waters.

During the first half of the Cold War, the United States actively deployed tactical nuclear weapons and their delivery systems on territories that now form part of Japan. This applied primarily to the Ryukyu Archipelago, including Okinawa, which was returned to Japanese sovereignty in 1972. U.S. nuclear weapons were also stationed on Iwo Jima and Chichijima, which had been transferred to Japanese jurisdiction somewhat earlier, in 1968. By the time these territories were ultimately returned to Japan, however, the United States had already withdrawn its nuclear weapons from them. In 1967, the government of Eisaku Satō proclaimed the Three Non-Nuclear Principles: Japan would "not possess, not produce, and not permit the introduction of" nuclear weapons (持たず、作らず、持ち込まさず).

The U.S.-Japan Extended Deterrence Dialogue was likewise established in 2010. Another mechanism for joint discussion of nuclear policy is the Security Consultative Committee, which operates in a "2+2" format, bringing together the foreign and defense ministries of Japan and the U.S. Department of State and Department of Defense. At the same time, the Republic of Korea's level of involvement in nuclear planning with the United States remains higher. This difference can be attributed to Japan's constitutional constraints and domestic public opinion, as well as to the distinct way in which the North Korean threat is perceived in Tokyo.

In February 2022, Shinzo Abe—who continued to wield considerable influence in Japanese politics even after leaving office—raised the possibility of discussing nuclear-sharing arrangements with the United States. Until then, the taboo surrounding such discussions, encapsulated in the phrase “giron sezu” (議論せず, literally "do not discuss"), was sometimes referred to in Japanese public discourse as an unofficial fourth Non-Nuclear Principle. One longer-term consequence was the signing of a broad package of defense agreements between Tokyo and Washington in April 2024. These arrangements provide for cooperation across a wide range of areas, from missile development and space activities to nuclear fusion.

In general, in recent years, Japan’s security policy has been characterized as militaristic; for example, the Self-Defense Forces’ right to retaliate was formalized with the revision of a number of strategic documents in December 2022. In November 2025, Prime Minister Sanae Takaichi did not explicitly reaffirm Japan's commitment to the Three Non-Nuclear Principles, giving rise to speculation that Tokyo might reconsider the foundations of its nuclear policy. Taken together with the lifting of restrictions on the export of lethal weaponry in April 2026, these developments point to a fundamental shift in Japanese strategy.

Australia and New Zealand: A Broken Triangle

The trilateral alliance between Australia, the United States, and New Zealand was formalized by the conclusion of the ANZUS Pact in 1951. Under Article IV, an attack on any one of the parties is considered a threat to the security of all. It is this provision that is generally regarded as the foundation of U.S. security guarantees to both countries.

Over time, however, the structure of the alliance underwent significant changes. The United States interpreted New Zealand's unilateral 1984 ban on visits by ships carrying not only nuclear weapons but also nuclear propulsion systems as a voluntary renunciation of U.S. positive security guarantees. Although Bill Clinton granted New Zealand the status of a major non-NATO ally in 1996, it was not until 2008 that Washington once again began referring to Wellington as an ally in its official rhetoric. New Zealand's foreign policy combines several seemingly disparate elements: participation in the 1971 Five Power Defense Arrangements and the Anglosphere intelligence alliance known as the Five Eyes, alongside involvement in the New Agenda Coalition and ratification of the Treaty on the Prohibition of Nuclear Weapons (TPNW).

Thus, of the two non-nuclear members of ANZUS, only Australia has remained under Washington's "nuclear umbrella." Although U.S. tactical nuclear weapons were never deployed on Australian territory, even during the Cold War, a number of critical command-and-control facilities were established there. These included the Pine Gap facility—which continues to operate under joint Australian-U.S. management—and the Joint Defense Facility Nurrungar (JDFN), which was closed in 1999. The purpose of these ground-based installations was to create an early-warning system for detecting missile launches. The nuclear dimension of security is addressed through the annual AUSMIN consultations, conducted in a "2+2" format since 1985. In addition, the two countries have held a Strategic Policy Dialogue since 2019.

In September 2021, the leaders of Australia, the United Kingdom, and the United States jointly announced the creation of AUKUS. The arrangement provides not only for equipping Australia with nuclear-powered submarines (a move that in itself sets a precedent for non-nuclear-weapon states) but also for trilateral cooperation on the development of a range of critical technologies, including artificial intelligence, quantum computing, and hypersonic weapons. One aspect of AUKUS that may be viewed as problematic from the perspective of the nuclear non-proliferation regime is the planned transfer of Virginia-class submarines to Australia at a later stage of the initiative. The issue is that the reactors powering these submarines use uranium enriched to 90%. At the same time, according to the action plan released in March 2023, the first SSN-AUKUS submarine is not expected to enter service with the Royal Australian Navy until the 2040s, assuming there are no further delays to the program.

Paradoxically, Australia remains a party to the Treaty of Rarotonga, which established a nuclear-weapon-free zone (NWFZ) in the South Pacific in 1985. Australia was also among the initiators of the 1996 Comprehensive Nuclear-Test-Ban Treaty and played an important role in the development of the model Additional Protocol to IAEA safeguards agreements in the late 1990s and early 2000s; the Commonwealth of Australia was the first state to sign such an agreement. At present, negotiations between Canberra and the IAEA concerning Article XIV of Australia's Comprehensive Safeguards Agreement remain ongoing. The central issue is the applicability of safeguards to enriched uranium, including for submarine nuclear power plants.

Major Non-NATO Allies: No Special Guarantees

In 2003, the United States designated several Asia-Pacific countries as Major Non-NATO Allies, including Thailand and the Philippines. However, despite their bilateral security arrangements with Washington, neither country was incorporated into the regional system of extended nuclear deterrence.

In this respect, the Philippines represents a unique case. Despite the 1951 Mutual Defense Treaty, the United States is generally not considered to extend a "nuclear umbrella" to Manila. U.S. tactical nuclear weapons were stationed in the Philippines from 1958 until at least 1977. Following the far-reaching domestic political changes of the 1980s, the country's non-nuclear status was enshrined in the 1987 Constitution, specifically in Article II, Section 8. At the same time, Washington has not missed the opportunity to capitalize on the current administration of Ferdinand Marcos Jr. to strengthen defense ties and further expand its military footprint in the country. In addition, Typhon missile launchers have been deployed in the Philippines since 2024, and in May 2026 a Tomahawk missile was launched from one of these systems for the first time on Philippine territory. Earlier variants of the Tomahawk were capable of carrying nuclear warheads.

Another important distinction from the states that form part of the extended nuclear deterrence system is that Thailand and the Philippines, as well as New Zealand, have signed and ratified the Treaty on the Prohibition of Nuclear Weapons (TPNW). Australia, the Republic of Korea, and Japan, by contrast, have not even moved to sign the treaty, largely out of concern over a possible negative reaction from their security guarantor.

Finally, it is worth considering the case of Taiwan, which China regards as its twenty-third province. In 2003, Washington granted the island de facto Major Non-NATO Ally status. The United States continues to adhere to a policy of strategic ambiguity toward Taipei and does not formally recognize Taiwan's independence. Nevertheless, U.S. tactical nuclear weapons were stationed on the island between 1960 and 1974. Today, the sale of advanced weapons systems to Taiwan remains a major source of friction in U.S.-China relations. It is still too early to judge whether Donald Trump's comparatively restrained rhetoric on Taiwan during his recent summit with Xi Jinping should be viewed as a tactical maneuver. By contrast, Joe Biden repeatedly spoke publicly about Washington's commitment to defend the island, even though the White House subsequently walked back those statements.

Alexey Stepanov:
Main Trends in the Development of China’s Missile and Nuclear Forces

A Festival of Nuclear Umbrellas

Thus, extended nuclear deterrence as applied to U.S. allies in Asia is far from a monolithic phenomenon. On the contrary, such guarantees are clearly heterogeneous: ranging from sporadic verbal assurances in the case of Taiwan to de facto joint nuclear planning with the Republic of Korea. Moreover, the level of guarantees extended to individual actors has varied significantly over time. The overt deployment of nuclear weapons and delivery systems on allied territory may give way to a guarantor's relative disengagement from the beneficiary's security concerns—a dynamic that is increasingly evident today. This phenomenon may be described as a “festival of nuclear umbrellas,” by analogy with the notion of a “patchwork quilt,” a term commonly used to characterize both the broader U.S. alliance architecture in the Asia-Pacific and the multiplicity of economic initiatives across the region.

Extended nuclear deterrence is, to a large extent, a conceptual construct whose effectiveness depends on a multitude of variables. Despite the absence of explicit references to the nuclear option in the numerous bilateral and minilateral agreements between the United States and its allies, prevailing interpretations of these arrangements tend to take extended nuclear deterrence as a given. This has led both to the institutionalization of various joint formats—from military exercises to nuclear planning groups, or at least coordination frameworks—and to the doctrinal entrenchment of the concept in the strategic documents of the United States and its allies. At the same time, fluctuations in the implementation of this form of deterrence only reinforce the argument that perceptions and threat assessments on the part of both the guarantor and the beneficiaries are of critical importance.

Unlike NATO arrangements, the Asia-Pacific has not seen the deployment of nuclear weapons on allied territory since 1991. A change in this approach remains unlikely in the short term, even amid the voluntarist policies pursued by the Trump administration. Moreover, whereas in Europe priority is given to the air leg of the U.S. nuclear triad—namely gravity bombs deliverable by dual-capable aircraft—in the Asia-Pacific greater significance attaches to the submarine component. This can be seen in such examples as AUKUS and visits by U.S. nuclear-powered submarines to South Korean ports.

At the same time, the European and Asian theatres exhibit an important similarity: in recent decades, the credibility dilemma surrounding U.S. security guarantees has become particularly acute. In Charles de Gaulle’s classic formulation, it is encapsulated in the question of whether Washington would be willing to “trade New York for Paris” in the event of a nuclear exchange. For America’s key partners in the Asia-Pacific, this logic remains equally relevant—it is enough simply to replace Paris with Tokyo, Seoul, Canberra, or Taipei. It is during Donald Trump’s second term that distrust of U.S. security guarantees has become even more pronounced, even if not necessarily expressed openly. This stems both from the broader instability of the international environment and from the unpredictability of the guarantor itself, manifested in the current Republican administration’s at times seemingly irrational foreign policy decisions.

In this regard, despite the additional guarantees formalized under Joe Biden (AUKUS in 2021, the agreements with the Republic of Korea in 2023, and those with Japan in 2024), it is possible to anticipate a further erosion of the extended nuclear deterrence system in the Asia-Pacific, albeit not as pronounced as in Europe. U.S. allies may increasingly take steps toward providing for their own security, though for now these efforts remain cautious and tentative. In the medium term, however, particularly if the strategic environment continues to deteriorate, it cannot be ruled out that the beneficiaries of U.S. security guarantees will pursue more systematic measures to strengthen their own security—whether unilaterally or through bilateral and multilateral arrangements, including in minilateral formats.