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US Allies and Nuclear Weapons Cooperation

Jeffrey Larsen

The United States maintains a national security strategy that recognises the distinctions between different regions of the world and appreciates the allies with whom it shares common values and worldviews. For many of America’s allies, this commitment includes US nuclear deterrence guarantees. US national security strategy highlights the importance of maintaining peace and security in the regions, ensuring the defence of close allies and partners, and negating the efforts of regional or global adversaries. This chapter examines and compares the extended deterrence arrangements in Europe with those in the Indo-Pacific. While there remain important differences between the two regions—most notably the degree of formal structure underpinning nuclear sharing in the North Atlantic Treaty Organization (NATO)—both sets of arrangements fulfill the key purpose of reassuring US allies that Washington would come to their assistance if their security was threatened.

The US has particularly longstanding linkages with the states of Europe. However, in the Indo-Pacific, it also has close relations with a number of democratic nations, including economic, political, trade and military partnerships. As one analyst has written, ‘the grave obligations associated with the US nuclear guarantees to Seoul and Tokyo are consistent with the high stakes the United States has in their safety from aggression’.¹ The same could be said regarding the member states of NATO, as well as additional allies in Europe, the Middle East and the Indo-Pacific.

Recent presidents have reiterated America’s commitment to its allies. President Barack Obama’s 2015 National Security Strategy defined America’s regional strategies as having a long-term affirmative agenda in each region, rather than focusing on immediate threats.² His administration pursued this agenda with the help of reinvigorated alliances with longstanding friends. In the Indo-Pacific, for example, this meant modernising the alliances with Japan, South Korea, Australia, the Philippines and Thailand, and using such regional institutions as the Association of Southeast Asian Nations (ASEAN), the East Asia Summit and the forum for Asia-Pacific Economic Cooperation (APEC). While recognising the rise of China and the need to be competitive, the Obama strategy rejected ‘the inevitability of confrontation’ with Beijing.³

Two years later, President Donald Trump’s administration published a new National Security Strategy that accepted many of these principles, but with a more assertive tone. In what is now called the Indo-Pacific, the US declared China to be an aggressive challenger to peace and security in the region. The strategy highlighted the importance of regional allies and promised to increase quadrilateral cooperation with Japan, Australia and India. It also highlighted the Philippines and Thailand as important allies; recognised the growing security and economic partnerships with Vietnam, Indonesia, Malaysia and Singapore; emphasised the importance of ASEAN and APEC; and stated that the US would maintain its close ties with Taiwan.⁴

The 2017 National Security Strategy also emphasised how closely the US and Europe were bound together, as exemplified in NATO. It stated that the US remained fully committed to NATO’s Article 5 commitment that an attack on one was an attack on all. The strategy highlighted threats to Europe that included a resurgent Russia, terrorism and growing Chinese influence in European affairs, and committed the US to retaining the necessary military capabilities in Europe to deal with such challenges.⁵

The 2018 Nuclear Posture Review (NPR) affirmed America’s commitment to the security of its allies and partners, tailored to the differing requirements of the two regions of greatest importance to the US. In the Asia-Pacific, the North Korean nuclear program and China’s more aggressive behaviour threaten key allies. Dealing with these threats includes extended deterrence and the assurance of America’s friends.⁶ While all America’s key allies in East Asia strongly supported the 2018 NPR, NATO allies accepted its premises with some uncertainty. Further, while they were pleased to see in its words a strong rebuttal of Russia, they were concerned about the continuing reliability of the US commitment given statements by President Trump.

Bilateral security arrangements are embedded in larger diplomatic, political and economic dealings with Asia. Traditionally, Washington had pushed for greater economic cooperation in the region, such as the Trans-Pacific Partnership. The US withdrew from this treaty in 2017. However, despite this withdrawal, the Trump administration supported the concept of ‘a free and open Indo-Pacific’—a proposal originated by Japanese Prime Minister Shinzo Abe. In late 2017 Abe also proposed a ‘democratic security diamond’, which led to meetings and cooperation among the so-called Quad.⁷

In his first round of telephone calls to allied leaders in late 2020, President-elect Joseph Biden confirmed that the US wanted to retain and enhance these linkages. He expressed his desire to strengthen alliances with South Korea and Japan—two countries he called the ‘cornerstones of a prosperous and secure Indo-Pacific region’.⁸

Tailored Extended Deterrence

As a sovereign, independent nation-state, the US’s primary national security goal is the protection of its own people, territory and interests. But it has also promised to protect many of its friends and allies around the world. This guarantee is accomplished by extending its nuclear and conventional umbrella over some 40 allies, nearly all of them non-nuclear weapon states.⁹

The concept of extended deterrence means that one state will provide security for another state through the threat of punishment against a third party that may wish to attack or coerce the second state. In short, extended deterrence commits the US to the possibility of going to war with another great power in order to protect a more vulnerable ally.¹⁰ This logical extrapolation of deterrence theory is a commitment that is not made lightly or offered to everyone.

Very different models of extended deterrence are found in different regions of the world.¹¹ Yet the US’s extended deterrence umbrella faces the same challenges in both Europe and Asia: it is invaluable for assuring allies of American support and commitment, but worrisome to allies who may doubt the credibility of a president actually committing those weapons to use when necessary. Credibility is enhanced by the visible presence of US service personnel and their families in allied countries, conventional weapon and missile defence deployments, and allies developing indigenous capabilities for self-defence and deterrence by denial.

Extended deterrence has served a number of additional purposes. For example, it has created caution among the nuclear players on the world stage and it may prevent nuclear proliferation by America’s allies. The nuclear umbrella has also served to reinforce the commitment of NATO states to the Nuclear Non-Proliferation Treaty—one example being West Germany, which was often touted as a potential nuclear weapon state during the 1950s and 1960s.¹² In return for a US security guarantee, NATO allies agreed not to pursue their own nuclear capabilities. A similar understanding was in place in North-East Asia for the purpose of containing proliferation pressures in Japan and South Korea.

In Asia, the US has longstanding security commitments to Japan through the US–Japan Security Pact.¹³ Both sides have always assumed that this means the possible use of US nuclear weapons to protect Japanese territorial sovereignty against potential aggression, Japan’s anti-nuclear stance notwithstanding. In 2009, the US secretary of state travelled to Japan to proclaim publicly that this solemn commitment to defend Japan was intact in the face of North Korean military threats.¹⁴

South Korea is also the recipient of the US nuclear security guarantee. The US and South Korea have maintained a mutual security arrangement since 1954, and US nuclear weapons were stationed in South Korea until 1992.¹⁵ Australia also assumes that the US nuclear umbrella extends over its territory, as part of the 1951 Australia, New Zealand, United States Security Treaty (ANZUS). Canberra has reiterated this belief in a succession of defence white papers.¹⁶

Nuclear weapons are likely to continue to play a central role in US security policy. The US has determined that providing security guarantees for its allies remains in its vital interests. Unlike the situation in Europe, where dual-capable aircraft stand ready to deliver American nuclear weapons in case of a crisis, North-East Asia benefits from American security guarantees without having any US nuclear weapons in the region. Deterrence, after all, is essentially psychological, working on the perceptions of the potential adversary.

Debates about allies developing their own nuclear weapons have occasionally risen to the surface. While many of the NATO allies have put such thoughts behind them, the concept has been raised relatively recently by the US itself, with President Trump musing about Japan and South Korea developing their own nuclear weapons to reduce US commitments and costs. Subsequently, and in response to concerns that the US might withdraw its extended deterrence umbrella, interest in developing nuclear programs gained some limited traction in those two countries.¹⁷ South Korea and Japan both worry about North Korea and its nuclear program, but Japan’s long-term concern is China and its growing military capability. Seoul and Tokyo are developing improved conventional strike capabilities and missile defence systems to supplement US forces and provide options below the nuclear threshold in case of conflict. These could simultaneously enhance deterrence while reducing reliance on the US nuclear guarantee.¹⁸ Some analysts even suggest that the US should allow ‘friendly proliferation’ of nuclear weapons to reduce its burden and enhance the credibility of such threats when they are brandished by those states most affected by neighbouring adversaries.¹⁹

However, as Brad Roberts has written:

The benefits of remaining a non-nuclear ally of the United States are high relative to the benefits of the available options, while the costs are relatively low. Thus, it is hardly surprising that no US ally has determined to have nuclear weapons of its own since the very earliest days of the Cold War.²⁰

The same calculation is in play in those states not explicitly under the guarantee of US extended nuclear deterrence. They see no better option than teaming with the US.

What do America’s non-nuclear allies want in return for their commitment to the US as their protector?²¹ In today’s world, many allies seek greater assurance from the US, given security trends and the rise of potentially adversarial powers in their region. Anxious allies favour a balanced approach, such as that posited by President Obama in his 2009 Prague speech, which called for reduced emphasis on nuclear weapons and doctrine while still accepting the need for an arsenal that was second to none.²² That said, some allies are also concerned by the possibility of further reductions in weapons by the US, given the need for Washington to deter both China and Russia.

The European Model: NATO and Formalised Risk and Burden Sharing

The US’s extended deterrence and assurance arrangements for NATO are well established. The US agreed to guarantee the security of the other members as long as all contributed to the general defence—a process called risk and burden sharing. This included the full weight of America’s military capabilities, including forward-deployed conventional forces and nuclear weapons; the creation of a nuclear planning group for the alliance, which meets regularly to discuss issues related to nuclear deterrence in a collaborative environment; and the sharing of nuclear missions and tasks with allies.²³ All members except France participate in the Nuclear Planning Group.

While acknowledging that the US defence posture in Europe has changed significantly since the end of the Cold War, the US recognises the regional and global importance of keeping significant military forces on the continent. This rationale includes maintaining a robust US military presence in Europe to deter the political intimidation of allies and partners, promote stability, demonstrate America’s commitment to NATO allies, build trust and goodwill among host nations, and facilitate multilateral operations in support of mutual security interests.²⁴

The presence of US nuclear weapons—combined with NATO’s nuclear-sharing arrangements under which some non-nuclear members possess specially configured aircraft capable of delivering nuclear weapons—contributes to alliance cohesion and provides reassurance to allies and partners who feel exposed to regional threats. The US has affirmed that it will not make unilateral decisions as to the future of those weapons or their basing in Europe, stating: ‘Any changes in NATO’s nuclear posture should only be taken after a thorough review within and decision by the Alliance’.²⁵ NATO’s 2012 Deterrence and Defence Posture Review determined that the alliance’s nuclear risk and burden-sharing arrangements were sufficient for NATO deterrence ‘under current circumstances’.²⁶ Given changes in the European threat environment since 2012, parts of that document are out of date, but its conclusions are still followed by the alliance.

The 2018 NPR listed specific steps that the US would undertake in cooperation with NATO allies to strengthen nuclear deterrence in Europe. These included enhancing the readiness, survivability and operational effectiveness of dual-capable aircraft, as well as modernisation programs to update existing aircraft and weapons; promoting the broadest possible participation in nuclear risk and burden-sharing efforts; enhancing training and education about the deterrence mission; and ensuring NATO’s nuclear command, control and communications systems were updated.²⁷

US policy under the Biden administration will focus on restoring close ties to America’s allies and NATO. After years of relations based on transactional and often vituperative demands, America’s allies in Europe, with few exceptions, are pleased to return to a more normal relationship with Washington.

The non-nuclear states of the alliance will play a role in all decisions on how to best respond to the multitude of security challenges facing Europe today, through their shared membership in the North Atlantic Council, the Nuclear Planning Group and the various bodies of the European Union as it develops a common defence and security policy for Europe. On the other hand, the alliance will face challenges keeping some member states in the non-nuclear fold. The US may have to enhance its extended deterrence guarantees to assure those allies of American security promises.

The Asian Model: Bilateral Defence Agreements

Allies in the Indo-Pacific lack a region-wide alliance structure akin to NATO in Europe. Extended deterrence in East Asia is a particularly complicated topic. A combination of differing cultures, divergent regional interests, historical animosities and the tyranny of geography prevents the creation of a pan-Pacific defence coalition. Evolving relationships and changing threat perceptions within the region, and different outlooks on US extended deterrence guarantees, make even a trilateral defence relationship between the US, Japan and South Korea an unlikely prospect. Assuring Indo-Pacific allies and partners holding disparate perspectives on national security requirements, and deterring regional adversaries, depends on the credibility of the US commitment and confidence on the part of both allies and adversaries that it will abide by those commitments. Working with the US to address common threats represents an important common denominator across the national security strategies of these disparate states.

Despite facing serious threats in the immediate neighbourhood, at least two of these states may have been prevented from developing their own nuclear weapons because of US extended deterrence. Japan and South Korea have dabbled with the idea of developing their own strategic deterrent weapons whenever they began to have doubts about the US guarantee.²⁸ Some analysts in those countries have called for even greater participation in plans, forces, deployments and exercises, similar to the involvement that US allies in NATO have via the alliance’s existing institutions.

The 2010 NPR stated:

In Asia and the Middle East—where there are no multilateral alliance structures analogous to NATO—the United States has maintained extended deterrence through bilateral alliances and security relationships and through its forward military presence and security guarantees.²⁹

This position remains unchanged. The US withdrew its forward-deployed nuclear weapons from the Pacific region at the end of the Cold War. Since then, it has relied on ‘its central strategic forces and the capacity to redeploy non-strategic nuclear systems in East Asia, if needed, in times of crisis’.³⁰

The Trump administration reiterated that ‘the US commitment to our allies and partners in the Asia-Pacific region is unwavering’. The alliance system in the region continues to be ‘a series of bilateral relationships with varying degrees of multilateral cooperation across different missions’.³¹ To ensure credible extended deterrence in the region, the US committed to maintaining integrated, flexible and adaptable nuclear and non-nuclear capabilities; investing in regional missile defences; demonstrating joint commitment through multinational exercises; and working together to ensure shared understandings of common threats and resulting deterrence requirements.

The strategy of maintaining a ‘continuous presence’ of US aircraft in the Indo-Pacific ensures that potential adversaries are always aware that the US has nuclear-capable forces in-theatre. This strategy, however, faces challenges from both allies and adversaries. Some politicians and commentators in Japan and South Korea, for example, have either argued for their own countries to develop an independent nuclear deterrent or called for the US to permanently station nuclear forces on their territory.³² These calls represent an implicit challenge to the assurance value of the continuous presence strategy and its reliance on nuclear-capable forces that are geographically distant from the countries they are intended to protect.

Japan faces a number of regional security challenges and turns to the US for assurance as its most important ally. The two governments agreed in 2011 to establish the Extended Deterrence Dialogue as a bilateral extended deterrence consultative mechanism to address a range of matters, such as Japan’s inclusion in the US nuclear umbrella.³³ The US–Japan Defence Cooperation Guidelines were revised in 2015 to reflect greater Japanese contributions to its own defence.³⁴

The US has maintained close defence ties with the Republic of Korea (ROK) since the Korean War. The 1953 ROK–US Mutual Defence Treaty pledges that any attack on either party will be met by a joint response to ‘meet the common danger’. In 2010, the US and South Korea established an Extended Deterrence Policy Committee as a formal mechanism for discussing deterrence matters.³⁵

In the case of Australia, the continued close engagement with the Indo-Pacific by the US is viewed as vital to both its national security and regional stability.³⁶ Under Article IV of the ANZUS Treaty, the US and Australia pledged:

That an armed attack in the Pacific Area on any of the Parties would be dangerous to its own peace and safety and declares that it would act to meet the common danger.

De facto, the US includes Australia under its nuclear umbrella. The Australian Government views US extended nuclear deterrence as a guarantee that has allowed the country to enjoy protection from nuclear attack without having to develop its own independent deterrent capability. It also believes that nuclear deterrence will become more relevant to Australia’s defence as the Chinese threat grows in coming years.³⁷

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The increasing demand on American military might in both Europe and the Indo-Pacific serves to highlight the continued need for close allies that represent strength in numbers and can provide conventional forces and missile defences that synergistically enhance the defence of these alliances. In both Europe and East Asia, the US welcomes inputs from allies into its extended deterrence strategies, including nuclear planning and policy. While this input is codified in longstanding institutions in NATO, it is conducted on a bilateral basis with allies in Asia. The objective in both regions, however, is the same: to assure America’s closest friends of the depth of its commitment to their security, and of the sense of obligation felt by the US to come to their aid in a crisis.

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