U.S. Extended Nuclear Deterrence: A Guide for the Perplexed

Michael Rühle, U.S. Extended Nuclear Deterrence: A Guide for the Perplexed, No. 667, August 5, 2026

Michael Rühle
Michael Rühle is the former Head of the Climate and Energy Security Section, NATO, and served for over 30 years in NATO’s international staff, specializing in policy planning, speechwriting, energy security, and hybrid threats.

In his final article, published in 1976, renowned U.S. strategist Bernard Brodie noted the stark contrast between the extensive literature on arms control and its disappointing real-world results.[1] Half a century later, Brodie’s comments still remain true. In fact, they can safely be extended to include nuclear nonproliferation and nuclear deterrence, including extended deterrence. In all these areas, one can observe what Brodie termed a “huge disparity between fullness of advice and leanness of practical results.” Much of what is written typically is either a regurgitation of well-known facts or emotional pleas to save the world from nuclear Armageddon.

The lack of new, sensible ideas should not come as a surprise. After all, until recently, the nuclear landscape has been much less volatile than predicted. No nuclear war has ever occurred, and the number of official and unofficial nuclear-armed nations remains in the single digits. Within the West, criticism of the military or moral flaws of nuclear deterrence has waxed and waned. However, overall, the logic of nuclear deterrence as an indispensable instrument of Western security policy has rarely been seriously questioned. The same held true for extended deterrence.

The United States is the only country that officially extends its nuclear deterrent to other nations, primarily allies in Europe and Asia.[3] Since the inception of this policy in the early 1950s, extended deterrence has served several purposes: demonstrating to allies that the United States is fully committed to their security; demonstrating to opponents that any attack on an ally might lead to a major U.S. response; and, relieving allied pressure to acquire nuclear arsenals of their own. Today, over 30 countries rely on the U.S. “nuclear umbrella.”

Time and time again, analysts have pointed out the contradictions inherent in a policy based on a seeming U.S. willingness to risk suicide for its allies. Consequently, some researchers have sought to demonstrate that extended deterrence is largely a politically convenient fiction.[4]  Most recently, two U.S. analysts argued that “regardless of who sits in the Oval Office, it is no longer sensible for the United States to wage a major nuclear war to help far-flung allies enmeshed in regional conflicts.”[5]

However, asking whether the United States would actually be willing to trade New York for London or Seoul (or whether a French President would trade Paris for Berlin) reveals a rather simplistic understanding of international politics in general and extended deterrence in particular. If the question is posed in such terms, the answer would always be “no”—as it should be, since the primary responsibility of any U.S. president (or French president or British prime minister) is to defend his or her own nation. U.S. extended deterrence has become a central part of the international order precisely because Washington and its allies have never defined this concept so categorically. For the United States and its allies, extended deterrence means that the United States will not rule out a nuclear response to an attack on its allies. Therefore, extended deterrence is one element of much broader political, military, and economic relationships, and it will rise and fall with the overall health of these relationships.[6]

Credibly making a defense promise, often mistakenly referred to as a “nuclear guarantee,” requires considerable military capabilities. Hence, the United States has maintained a larger nuclear arsenal than would be required to solely deter an attack on the homeland. For decades, therefore, arms controllers scoffed at this construct, with some advocating an end to extended deterrence because it prevented the United States from ever seriously contemplating eliminating nuclear weapons.[7] Although the idea of nuclear abolition has long lost traction, parts of the U.S. analytical community continue to regard reductions in nuclear arsenals as the goal that should trump all other considerations.[8]

U.S. extended deterrence was never meant to be a free service to allies. In Europe, in particular, allies have been keen to play their role, both to demonstrate their readiness to share risks and burdens in the nuclear domain, and to make their voices heard in nuclear deliberations. In NATO, extended deterrence thus took the form of “nuclear sharing,” which includes stationing U.S. warheads in Europe to be delivered by European fighters and crews in wartime. Other allies would support this nuclear mission by suppressing enemy air defenses, for example. In Asia, where no NATO-like body exists, the United States did not replicate the European model. However, it has offered more intensive consultations, somewhat akin to NATO’s Nuclear Planning Group.

In both regions, extended deterrence has always been understood to have a strong nonproliferation aspect. In fact, the relationship between U.S. extended deterrence and nonproliferation is too significant to dismiss. For example, West Germany initially resisted U.S. pressure to join the Nuclear Non-Proliferation Treaty (NPT) as a non-nuclear country because it feared being relegated to second-class status. Therefore, when it signed the NPT in 1969, it made signing contingent on the continuation of U.S. extended deterrence.[9] In 2022, immediately after Russia’s attack on Ukraine, Germany ordered new F-35 fighter aircraft to maintain its nuclear-sharing arrangements with the United States. In Asia, growing nervousness about China’s military buildup and the threat posed by North Korea has sparked debates in Japan and South Korea about a national nuclear program.

These developments suggest that, when countries perceive major threats to their security, their stance on nuclear weapons is shaped by their immediate political concerns rather than virtuous universal nonproliferation norms. It also suggests that U.S. extended deterrence, if clearly articulated and sustained by commensurate military capabilities, dampens the nuclear ambitions of allies and strengthens nuclear nonproliferation, irrespective of its credibility dilemmas.

Given the Trump Administration’s mixed messages about America’s future role in allied security, some analysts are looking for alternatives to the U.S. nuclear umbrella. As far as Europe is concerned, under current circumstances, the likelihood of individual states initiating national nuclear weapons programs remains low. The most plausible way forward for non-nuclear allies seems to be engaging in a nuclear dialogue with France. Paris had offered such a dialogue for some time, though never implying that it would lead to a nuclear umbrella over Europe. In March 2026, President Macron unveiled his concept of “dissuasion avancée” (forward deterrence), which includes occasional deployments of French nuclear-capable fighters to allied air bases, nuclear dialogue with interested allies, and allied participation in French nuclear exercises.[10] While these proposals may appeal to France’s long-standing ambition to be a leader in European defense, Paris has made it clear that “forward deterrence” is not meant to replace NATO’s sharing mechanisms. Above all, the fundamental dilemma of extended deterrence—whether French or American—remains: the final decision to use nuclear weapons rests with each country’s president.

Some analysts deem this purely national focus insufficient and have suggested work-arounds. A German political science professor gained notoriety by proposing a “nuclear suitcase” that would circulate among the larger European Union countries.[11] Recently, two U.S. analysts suggested “expanding the list of countries that hold the keys to NATO’s nuclear arsenal” by creating arrangements that would enable France and Britain, in times of crisis, to “release” some of their air-delivered nuclear weapons to other allies. In such a “three-key system,” the deterrent “would be operational if any of the three leaders – of France, the United Kingdom, or the United States—were to give the go-ahead.”[12] This arrangement is meant to address the issue of a United States that is unwilling to push the button. However, how likely is it that France would launch nuclear weapons in a NATO context, even if the other two nuclear powers were opposed? As with the case of the rotating “nuclear suitcase,” such attempts to circumvent national prerogatives lead to unrealistic proposals.  The authors call out the long-recognized U.S. credibility dilemma, but ultimately offer no solution other than more nuclear proliferation—neither a new suggestion,[13] nor without its own great risks.

The quest for originality over realism also extends to Asia. U.S. isolationists have long argued that if Japan and South Korea wanted to develop nuclear weapons, Washington should simply give them its blessing.[14] This idea is now resurfacing in a different guise. Having effectively dismissed extended deterrence as an outdated Cold War concept, Jennifer Lind and Daryl Press argue that if South Korea were to request a nuclear-sharing arrangement with the United States, Washington should respond positively. However, it remains unclear why Seoul should enter into such an arrangement when the authors themselves have concluded that the U.S. umbrella to be incredible and “broken.” Even more, should Seoul build its own nuclear weapons, the authors suggest that “the United States should help Seoul acquire them safely.” Although the authors consider extended deterrence to be a “bluff,” they suggest that “Washington could strengthen extended deterrence during the transition period in which South Korea becomes nuclear by temporarily positioning tactical nuclear weapons on the peninsula and redeploying American troops closer to the demilitarized zone.”[15] Apparently, to safely dismantle extended deterrence, one must first try to strengthen it.

No matter the analytical twists and turns of academic experts, all alternatives to U.S. extended nuclear deterrence look weak. A “Europeanized” nuclear deterrence model based on the French and possibly British arsenals offers far less in terms of quantity and quality than the U.S.-centered system, which also has the full weight of American conventional power behind it. The European Union cannot develop a common nuclear policy because Austria and Ireland have signed the Treaty on the Prohibition of Nuclear Weapons (TPNW), which deems nuclear weapons and deterrence illegal. If some nations were to initiate national nuclear programs, mistrust among European countries would grow to the point of jeopardizing the entire European project. Until now, at least, the United States shared this view, because the prospect of dealing with a multi-nuclear Europe and a multi-nuclear Asia seemed too horrific to contemplate.

Extended deterrence suffers from many paradoxes. It involves making promises that may bolster deterrence in peacetime but that one would hesitate to fulfill once deterrence has failed. It attributes deterrence and reassurance functions to certain weapon systems that allies may believe in, but that opponents may not. It also rests on the paradox that one state’s nuclear arsenal serves to uphold the non-nuclear weapons status of others.

Yet, despite these paradoxes, allies appreciate the “U.S. umbrella” and are trying to sustain it. It is easy to see why. Nuclear abstinence of many wealthy states in key geopolitical regions is neither a natural state of affairs nor the result of the Nuclear Nonproliferation Treaty—it is a consequence of U.S. extended deterrence. Many states stopped worrying about getting their own bomb because the United States assured them that it was unnecessary. Consequently, it is no coincidence that renewed interest in national or multinational nuclear options is resurfacing just as the United States appears to be questioning its international engagements. Reducing or ending America’s role as a nuclear protector could result in the largest wave of proliferation since the dawn of the nuclear era.

For these reasons, allied governments are unlikely to question the U.S. nuclear umbrella as long as Washington does not, and as long as the United States maintains more than a mere token conventional military presence in Europe and Asia. By contrast, “fixing” an umbrella in the ways suggested by prominent academics would likely result in a much more unpredictable and dangerous world.

This article appeared originally at National Institute for Public Policy (NIPP).

image: Between 13 and 24 October 2025, NATO held its annual nuclear exercise, Steadfast Noon, involving more than 70 aircraft from 14 Allied countries, including dual-capable aircraft (DCA) that can carry and deliver nuclear warheads. (U.S. Air Force)

[1] Bernard Brodie, “On the Objectives of Arms Control,” International Security, Vol. 1, No. 1, Summer 1976, pp. 17-36.

[2] See “Remarks by Under Secretary of War for Policy Elbridge Colby at the NATO Defense Ministerial (As Prepared),” February 12, 2026, https://www.war.gov/News/Speeches/Speech/Article/4404801/remarks-by-under-secretary-of-war-for-policy-elbridge-colby-at-the-nato-defense/.

[3] Russia’s nuclear relationship with Belarus is not considered an example of “extended deterrence” because Minsk does not seem to have much of a say in these arrangements.

[4] See Benoit Pelopidas, “The Nuclear Straitjacket: American Extended Deterrence and Nonproliferation,” Stefanie von Hlatky and Andreas Wenger (Eds.), The Future of Extended Deterrence: The United States, NATO, and Beyond (Washington, D.C.: Georgetown University Press, 2015), pp. 73-106.

[5] Jennifer Lind and Daryl G. Press, “The Broken Nuclear Umbrella: What Comes After Extended Deterrence,” Foreign Affairs, Vol. 195, No. 4, July/August 2026, https://www.foreignaffairs.com/issues/2026/105/4.

[6] The perception of extended deterrence as a building block of broader relationships is particularly well documented with respect to the Asian allies.  See Terence Roehrig, “Japan, South Korea, and the United States Nuclear Umbrella: Deterrence After the Cold War” (New York: Columbia University Press, 2017).

[7] See Barry Blechman, “Policy Forum 09-066: Extended Deterrence: Cutting Edge of the Debate on Nuclear Policy,” August 13, 2009, https://nautilus.org/napsnet/napsnet-policy-forum/extended-deterrence-cutting-edge-of-the-debate-on-nuclear-policy/.

[8] See Rose Gottemoeller, “The Strange Defeat of Nuclear Deterrence And the Coming Crisis in Strategic Stability,” Foreign Affairs, Vol. 195, No. 4, July/August 2026, https://www.foreignaffairs.com/ukraine/strange-defeat-nuclear-deterrence-rose-gottemoeller.

[9] See Michael Rühle, “Germany and Extended Deterrence,” Journal of Policy & Strategy, Vol. 4, No. 3, 2024, pp. 19-38, https://nipp.org/wp-content/uploads/2024/09/Analysis-Ruhle-4.3.pdf.

[10] See Astrid Chevreuil, “Macron’s Île-Longue Speech: Updating France’s Nuclear Doctrine for a New Era,” CSIS Commentary, March 4, 2026, https://www.csis.org/analysis/macrons-ile-longue-speech-updating-frances-nuclear-doctrine-new-era.

[11] See the interview with Herfried Münkler, „Europäische Atombombe wäre entscheidender Schritt hin zur eigenen Abschreckungskraft,“ Die Welt (online), January 2, 2024, https://www.welt.de/politik/deutschland/plus249280690/Herfried-Muenkler-Europaeische-Atombombe-waere-entscheidender-Schritt.html.

[12] Lind and Press, op. cit.

[13] See for example, Kenneth Waltz, “The Spread of Nuclear Weapons:  More May be Better,” Adelphi Papers, No. 171 (London, IISS, 1981).

[14] See Doug Bandow, “Let South Korea Build the Bomb. President Trump should allow Seoul to develop nuclear weapons in return for ending America’s security guarantee,” CATO Commentary, February 6, 2025, https://www.cato.org/commentary/let-south-korea-build-bomb.

[15] Lind and Press, op. cit.

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