Dr. Jennifer Bradley/U.S. Strategic Command
Most people don’t remember a time when the United States was not allied with NATO, Australia, Japan and South Korea. As these alliances span more than seven decades, it’s easy to take for granted that the relationships will continue. In fact, this phenomenon is not as common as it may seem, as only a handful of alliances have had this kind of longevity in the modern era.
These alliances are based on shared values, common interests and mutual threats. They have had the safe, effective and reliable nuclear deterrent of the U.S. throughout the decades to serve as the cornerstone of security guarantees. The changing security landscape and the emergence of the two-peer nuclear environment will challenge extended deterrence in ways not yet understood. This requires reexamining deterrence strategies and potentially acquiring new capabilities to effectively support Allies and close the growing “assurance gap.”
Safeguarding Against Threats
The U.S. policy of extended deterrence grew out of the overwhelming conventional threat the Soviet Union posed to Western Europe at the dawn of the Cold War. To defend against Soviet invasion and expansion, the U.S. extended its nuclear deterrence abroad. NATO was created as a nuclear alliance in 1949. U.S. nuclear forces deployed to NATO serving as the foundation of the defense agreement. The policy of extended deterrence reached beyond Europe. To deter growing threats from the People’s Republic of China (PRC) and North Korea in the Indo-Pacific, for example, the U.S. nuclear umbrella expanded to include Australia, Japan and South Korea, with U.S. nuclear weapons deployed to South Korea, though without NATO-style nuclear-sharing arrangements and fully under U.S. control.
The policy of extended deterrence remains a key component of the security strategy of the U.S. and its Allies. The 2022 Nuclear Posture Review affirms the U.S. commitment to extended deterrence, stating that the U.S. would “[ensure] our strategic deterrent remains safe, secure and effective, and our extended deterrence commitments remain strong and credible.” Furthermore, Allies under the nuclear umbrella have reiterated the importance of the U.S. role in extended nuclear deterrence for their security. The secretary general’s 2022 annual report reaffirmed NATO’s status as a nuclear alliance, stating, “As long as nuclear weapons exist, NATO will remain a nuclear alliance.”
In 2023, the Washington Declaration affirmed that South Korea “has full confidence in U.S. extended deterrence commitments and recognizes the importance, necessity, and benefit of its enduring reliance on the U.S. nuclear deterrent.” Japan’s Defense White Paper provides a summary of a Japan-U.S. defense ministerial meeting in which Tokyo “stated that bilateral efforts at various levels to ensure nuclear deterrence remains credible and resilient [are] more important than ever under the current international security situation.” Also, Australia’s National Defence Strategic Review states, “In our current strategic circumstances, the risk of nuclear escalation must be regarded as real. Our best protection against the risk of nuclear escalation is [U.S.] extended nuclear deterrence.”
The U.S. and its Allies remain committed to extended deterrence, but changes in the security environment mandate a review of the consultative mechanisms and the forces available, as they remain largely unchanged from adjustments after the conclusion of the Cold War. At that time, forward deploying nuclear weapons into Europe and the Indo-Pacific gave credibility to extended nuclear deterrence. However, as the security environment changed after the collapse of the Soviet Union, the U.S. shrank its nuclear footprint, returning most of its nuclear weapons from Europe and retiring the Tomahawk nuclear sea-launched cruise missile. While these decisions made sense for the security environment that they were made in, that era has passed. Renewed focus on ensuring the credibility of extended deterrence is necessary to assure Allies of their security in a changing security environment.
Challenges to Extended Deterrence
Russia’s February 2022 invasion of Ukraine brought into sharp relief the challenges that the U.S. and its Allies face from revisionist powers dissatisfied with the international system. Threatening the use of nuclear weapons against both NATO and non-NATO states has become commonplace for Russian officials — a threat made credible by a robust nuclear modernization program focused on improving existing forces and developing novel capabilities. More concerning, the poor performance of Russian conventional forces in Ukraine may lead Russian military strategists to rely more heavily on Russia’s expansive tactical and strategic nuclear capabilities to compensate for weakness in its conventional forces.
While the prospects of the PRC’s insistent claims to Taiwan as its territory have dominated security analysis in the past few years, Beijing’s ambitions extend much further and include reforming the global governance system to be more in line with its interests. These interests include establishing its own sphere of influence, which places the PRC at odds not only with its regional neighbors concerned about their sovereignty and access to natural resources but also with nations committed to the rules-based international order. The revelation of Chinese ambitions has been underscored by full-scale conventional and nuclear modernization and expansion. Due to a lack of transparency, Beijing’s intentions for its nuclear force remain opaque. However, “Military and Security Developments Involving the People’s Republic of China,” an annual U.S. Department of Defense report, increases its estimate of the future size of the PRC’s nuclear arsenal, with the 2022 report stating that the PRC could possess a nuclear stockpile of 1,500 weapons by 2035. The Chinese had 500 operational nuclear warheads as of May 2023, according to a U.S. Defense Department annual report on the Chinese Communist Party’s military and security developments. The rapid growth of the PRC’s nuclear arsenal allows it to adapt its nuclear strategy in any way it deems necessary to address its security concerns and achieve strategic objectives.
When comparing the challenges posed by the PRC and Russia to those of North Korea, it is tempting to diminish the threat because it is not to the same scale. That could be a mistake. Continued advancements in North Korean missile technology and growth of its nuclear force means that it poses a credible threat to the homelands of the U.S. and its Indo-Pacific Allies and Partners. Moreover, North Korea’s nuclear doctrine calls for “preemptive and offensive nuclear strike,” with credible nuclear forces capable of preemptive attack and nuclear warfighting. Coupled with North Korea’s history of provocation, the potential for miscalculation on the Korean Peninsula continues to increase.
While it is customary to examine each threat separately, the threats become more acute when examined together. Furthermore, strategists must consider the potential for these adversaries to work in unison to achieve their aspirations, especially given that each adversary considers the U.S. and its Allies and Partners as security threats and an impediment to achieving its national security objectives. Before Russia’s invasion of Ukraine, the PRC and Russia released a communique describing their relationship as a no-limits friendship. While the latest communique reframed the relationship as a “comprehensive partnership,” what is clear is that cooperation between these two states will continue and grow for the foreseeable future. While North Korea’s relationship with the PRC and Russia has often been volatile, with North Korea always careful not to become overly reliant on — and therefore vulnerable to — both nations, recently it has increased its overtures of cooperation to build strategic partnerships with both the PRC and Russia. The prospect of cooperation and potentially collaboration between or among these nations will challenge extended deterrence in the decades ahead.
The Assurance Challenge
The terms “extended deterrence” and “assurance” are often used interchangeably. While the concepts are related, they are focused on different audiences. Extended deterrence is directed at influencing adversaries to prevent attacks on Allies, while assurance is directed at convincing Allies and Partners of U.S. commitment to their defense. Just as deterrence is a cognitive function in the mind of the adversary, assurance is a cognitive function in the mind of the Ally. Both rely on perceptions of the capability, credibility and will of the U.S. to defend its vital interests and meet its security obligations.
Assuring Allies and Partners is inherently difficult. While economist Thomas Schelling’s Nobel Prize-winning research on deterrence described the benefits of uncertainty or “the threat that leaves something to chance” for deterrence, assurance of Allies and Partners requires a greater level of certainty and credibility. Allies are unwilling to leave their security to chance, nor should they be expected to. Analysts and policymakers have deliberated this challenge for decades, debating the question, “Would the United States sacrifice San Francisco for Tokyo or Boston for Prague?” It is a question that generates tremendous anxiety for the Allies under the nuclear umbrella because their security depends on the answer.
This anxiety is made substantially worse because the most likely pathways for potential nuclear use begin with regional conventional conflict escalating to limited nuclear use, meaning that the U.S.’s Allies and Partners are on the frontlines for this threat. Compounding this anxiety are the investments both the PRC and Russia have made in low-yield theater nuclear weapons. These weapons can hold the U.S.’s Allies and Partners at risk and grow North Korea’s nuclear arsenal while potentially lowering the threshold for use. Furthermore, deterring opportunistic aggression in one theater while the U.S. is fully engaged in another will challenge extended deterrence, heightening the anxiety of Allies and Partners and decreasing their confidence in extended deterrence meeting their security needs.
Risk to the Nonproliferation Agenda
The 2022 National Defense Strategy reiterates the U.S. commitment to nonproliferation of nuclear weapons, a commitment the U.S. has held since the mid-20th century. A key driver for providing a nuclear umbrella for Allies and Partners was to reduce the necessity for them to develop their own nuclear capabilities to meet their security needs. This allowed Allies and Partners to forgo their nuclear ambitions and accede to the Nuclear Non-Proliferation Treaty as nonnuclear states, strengthening the nonproliferation regime. In fact, the U.S. State Department has said, “Nuclear umbrella security agreements, whether unilateral or multilateral, have been, and are expected to continue to be, effective deterrents to proliferation.” The risk if Allies under the nuclear umbrella lose confidence in extended deterrence, determining that their security needs are no longer met by U.S. guarantees, could potentially put pressure on Allies to develop their own nuclear weapons, undermining the nonproliferation regime.
Recently, this risk has become more acute. South Korean President Yoon Suk Yeol suggested in 2023 that his country may consider building its own nuclear weapons to confront its deteriorating security environment. These suggestions came after the announcement that South Korea would establish its own strategic command in 2024 to address the North Korean nuclear threat and commanding the South’s strategic forces, to include conventional ballistic missiles, missile defenses, and space and cyber capabilities. These moves have been popular with the public, and polling suggests the South Korean public overwhelmingly supports the country’s acquisition of its own nuclear deterrent.
While South Korea has the most public support for developing a nuclear capability, it is not the only nation under the nuclear umbrella contemplating such a move. Some in the Japanese government have been forward leaning. Former Japanese Defense Minister Shigeru Ishiba, for example, stated in 2017, “Japan should have the technology to build a nuclear weapon if it wants to do so.” These nations are more than technically capable of developing nuclear weapons, but political considerations have served as a restraint. As those political considerations continue to change, they may transform into a catalyst for proliferation.
Mitigating the Risk to Assurance
Assuring U.S. Allies and Partners is an imperative, not only for the health of the nonproliferation regime but also for the continued strength of the alliance relationships. The U.S. benefits from strong alliances. These relationships contribute to global stability and prosperity by binding powerful nations together with a shared vision and purpose. Also, by building militaries that are interoperable and exercising in peacetime, these alliance relationships increase the involved nations’ overall military strength, thus enhancing deterrence. Failing to mitigate the risk to assurance could introduce stress into the alliances, undermining cooperation and creating the potential for global instability with the increased risk of arms races and growing competition.
To address the challenge, the U.S. must remain committed to the nuclear modernization program. The potential for productive relationships with the PRC and Russia, the focus on the war on terror and continued conflicts in the Middle East resulted in nuclear modernization delays. While the programs are now under way, any delay in funding or technical issues may result in an increase in risk.
While it is crucial that the modernization program stays on track, the decisions for the program were made in 2010, in a more benign security environment. Since then, the PRC’s strategic breakout, North Korea’s continued advancement of nuclear weapons and Russia’s increased aggression have prompted the U.S. and its Allies and Partners to reevaluate their strategies to confront these new security threats. NATO has begun that process with the Vilnius Summit Communique, announcing a new generation of strategic plans to increase readiness and improve deterrence of threats. However, any new strategy must address the risk to extended deterrence of the two-peer environment and the risk of opportunistic aggression from one adversary if the United States is engaged with the other. Therefore, any strategy for Europe must consider the risk of opportunistic aggression in the Indo-Pacific region and vice versa. This will place additional demands on both the U.S. and its Allies and Partners to ensure an effective deterrent.
Although it is tempting to immediately discuss the capabilities needed for extended deterrence and assurance, ensuring that the strategy is sound is a necessary first step. This leads to a more fruitful debate on the capabilities needed to make the strategy credible. While each leg of the triad is being replaced, a mix of both conventional and nuclear capabilities is necessary to meet both the military and political requirements for extended deterrence. Militarily, the forces must be survivable and prompt while also capable of holding adversary targets at risk. Strategically, the forces must provide a persistent presence and be visible to the adversary while also being acceptable to the ally and potentially providing the option for burden sharing. Through consultations, the U.S. and its Allies and Partners should develop a suite of capabilities to make extended deterrence strategies credible. Working directly with Allies and Partners will also enhance assurance.
Consulting with Allies is imperative for assurance, and to that end, the U.S. is modernizing and enhancing the processes for consultations within the alliances. Today, these processes are quite different between the Indo-Pacific Allies and the NATO Allies. There may be benefits in creating NATO-like consultative mechanisms and processes for the Indo-Pacific Allies. This would increase assurance by ensuring Allies feel that they are actively involved in decisions affecting their security. Additionally, building mechanisms to conduct combined deterrence planning across deterrence periods and spectrums of conflict will better allow the alliances to integrate deterrence operations. The Washington Declaration has laid the foundation for building these mechanisms with South Korea, announcing the establishment of a Nuclear Consultative Group charged with increasing nuclear dialogue, information-sharing and strategic planning. Finally, the security environment necessitates that NATO Allies and Indo-Pacific Allies work together to address security threats. Strengthening relationships across regions and nations will enhance deterrence throughout an increasingly interconnected security environment.
Conclusion
The grand bargain of extended deterrence is a unique aspect of U.S. alliance relationships. Elaine Bunn, the former deputy assistant secretary for Nuclear and Missile Defense Policy, testified before the U.S. Congress on this phenomenon, remarking, “I have come to believe that extended deterrence is amazing from both sides. We have our non-nuclear Allies, who have forsworn their own nuclear weapons and rely on another country, the U.S., in high-end situations, including nuclear attacks on their own territory and people. And it is amazing that the U.S. takes on the risk and responsibility of putting its own forces, even its population and territory, at risk on behalf of an Ally. And that is an amazing fact to the point that some, in the past, have found it incredible.”
The emerging two-peer environment will increasingly challenge this “amazing” agreement.
Our potential adversaries directly test the credibility of extended deterrence as they pursue goals that challenge the security of the U.S. and its Allies and Partners. The consequences of failing to assure Allies and Partners could dramatically change the international environment. Failing to address the challenges to assurance increases the risk of nuclear proliferation by Allies. “The credibility of our extended deterrence commitments is not only part of the nation’s ironclad commitment to our Allies, but it’s also essential in limiting proliferation of nuclear weapons,” Gen. Anthony Cotton, Commander of U.S. Strategic Command, told U.S. lawmakers.
Mitigating this risk requires reexamining our strategies and designing an extended deterrence posture with both conventional and nuclear weapons to achieve that strategy while modernizing the alliance structures and consultative mechanisms that increase alliance integration. This requires the U.S. to be open and increase consultations, especially with its East Asian Allies, on nuclear deterrence strategies and their respective employment.
Every conflict the U.S. has fought since World War I has involved Allies. They are the U.S.’s greatest asset, and it is easy to take this system for granted because of the longevity of the relationships. However, in the next decades, the challenges to extended deterrence and assurance will increase. The U.S. needs to take proactive action now to enhance extended deterrence and mitigate the risk to assurance to assure its Allies and Partners that the U.S. commitment is ironclad. Failing to close the gap might have consequences that could dramatically reshape the security environment. During World War II, British Prime Minister Winston Churchill observed, “There is only one thing worse than fighting with Allies and that is fighting without them.” By placing alliances on a solid footing for decades to come, prioritizing extended deterrence and assurance will ensure that the U.S. does not face Churchill’s worst-case scenario.
This article originally published in the Joint Force Quarterly, Issue 112, 1st Quarter 2024 magazine edition. It has been edited to fit Sentry’s format. Access the original version in full at https://ndupress.ndu.edu/JFQ/Joint-Force-Quarterly-112.aspx.