In the days and weeks ahead, their initial posts will be followed by other solicited contributions from prominent security thinkers and practitioners. We will also open up to the debate to readers and give the original contributors opportunity to reply and expand on their arguments. If you have your own views on the subject, please send them to Sam Roggeveen, editor of The Interpreter.

As the debate progresses, we will be interested in exploring not only the core analytical question of whether END is dead or alive, but also the policy options for the nations concerned, including those US allies who have sometimes entertained nuclear options of their own.

It should prove a fascinating, important and at times confronting conversation. 

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user Paul [W] Campbell.

In cases where the potential aggressor wields nuclear weapons, this means that the threat must be sufficiently grave for the deterrer to risk escalation to nuclear war, with the potential result of mutual suicide. It is not credible to take such mortal risks unless the alternative would also threaten one's existence or, in the case of allies, one's identity and viability as a great power. 

Therefore, extended nuclear deterrence should only be relevant against threats of such magnitude that the possible use of nuclear weapons to deter or defeat them would be proportionate. Against lesser threats, other means of deterrence must be relied upon. In East Asia today, this means, for example, that nuclear weapons should not be expected to deter potential Chinese efforts to occupy disputed islands in the South and East China seas, or to deter most probable forms of cyber disruption or political-economic bullying. Other means, including strengthened combined-allied conventional forces and operations, should be enhanced for these purposes.

The DPRK is a particularly troubling case. What scale and type of aggression by Pyongyang would credibly justify and call for US nuclear retaliation (including pre-emptively)? The US can destroy North Korea's military and economy, albeit at enormous costs not only to North Korea but also to South Korea. But the underlying challenge then (and now) is to replace the government in North Korea by one that is civilized to its own people and others. Nuclear weapons offer little to this end.

In the nuclear age, revisionist states, insurgents, and terrorists have learned to utilise asymmetric 'weapons' to fight more powerful nuclear-armed states. Nuclear weapons will remain for the foreseeable future in the background to deter existential-scale threats, but other means must occupy the foreground. Rather than wishing for nuclear weapons to do the job, or hand-wringing that they cannot, we should concentrate on developing credible strategies and capabilities to deter insidious new forms of aggression and subversion.

There is no material reason to think that US interest in moving gradually and multilaterally toward a world in which no one possesses nuclear weapons should undermine extended nuclear deterrence. The US is emphatically clear that, as long as anyone has nuclear weapons, and the nonproliferation regime is not extremely robust, the US will retain nuclear weapons and a state-of-the-art nuclear infrastructure. 

US interest in nuclear disarmament stems from the perception that a world without nuclear weapons would give it a greater advantage against others that might threaten it or its allies.  The others – particularly China, Russia and North Korea – recognize this! They see the Obama agenda as a means of strengthening the US advantage. Hence they (and Pakistan) are likely to impede nuclear disarmament. How does this weaken extended nuclear deterrence?           

It is easy to raise questions about the viability of extended nuclear deterrence in a vacuum, forgetting that nuclear deterrence comes with the real risk that the weapons will be used. Serious policy-making should focus on how to redress insecurities and deter and prevent war without the catastrophic risks of nuclear proliferation and use. The US is committed to leading in this direction. It would welcome similarly serious efforts by other influential states to address these underlying political-security challenges.

 

Photo courtesy of Wikipedia.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

The usefulness of extended deterrence for non-proliferation can hardly be debated. A large body of historical evidence shows that it was the key to the renunciation of nuclear weapons by many Western countries. And if Iran was to cross the nuclear threshold, a strong reaffirmation of US guarantees will be helpful to prevent countries such as Turkey and Saudi Arabia looking for alternative options.

Extended deterrence is, however, changing. Due to technological progress, force reductions, as well as a growing allergy in many countries to nuclear weapons, it increasingly relies on non-nuclear assets such as missile defense and long-range precision strikes. Conversely, due to the evolution of the strategic landscape, it is  geared towards preventing nuclear and other WMD threats more than conventional invasion.

The fact that extended deterrence will rely more on non-nuclear means will not necessarily make it less credible. As long as a state possesses nuclear weapons, its adversary has to take into account the risk, however remote, that he could ultimately face nuclear retaliation. And an emphasis on non-nuclear capabilities may in fact increase its effectiveness – relying too much on nuclear weapons can lead adversaries and allies to doubt the protector's resolve, and he himself may be 'self-deterred'.

Likewise, the fact that extended deterrence relies less on in-theatre means does not necessarily affect its credibility; deterrence is fundamentally a psychological process.

However, this also means that extended deterrence will have to be even more carefully nurtured than in the past. This is a complex exercise since it has to be credible in the eyes of three parties: the protector, the protected, and the adversary. There have been many examples of failures of extended deterrence in the past – the most egregious of which was the North Korean attack in 1950. But nowadays, the perception that Western countries are 'weak' is widespread. This can affect the value of deterrence both in the eyes of allies and of adversaries.

This calls for careful calibration of statements and declarations regarding security commitments, adapting them to various regional contexts and domestic sensitivities. This also calls for caution when decisions to alter a military posture are made for financial, political or ideological reasons – both allies and adversaries are watching.

A topical example is Europe, where many consider that nuclear weapons could be replaced with missile defense, and argue that what matters is a physical US military presence on the continent. But other believe that the withdrawal of US nuclear weapons could make the NATO deterrent less credible in the eyes of Russia or Iran, or encourage a Turkish nuclear program. (The withdrawal of US nuclear weapons from North-East Asia in 1992, largely conceived as a goodwill gesture towards Pyongyang, did nothing to prevent North Korea from going nuclear.)

Finally, Western countries should remember that the way they manage their commitments in one part of the globe can have a much broader impact. End-game decisions regarding operations in Iraq and Afghanistan, for instance, will be watched very carefully by both friends and foes.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user ♥Unlimited.

Recent trends seem to indicate the acceleration of the irrelevance of extended nuclear deterrence. If Pyongyang might not have been completely responsible for sinking the Cheonan, at least it didn't mind US extended deterrence for South Korea when it launched its artillery barrage against Yeonpyeong. The US didn't dispatch USS George Washington to the West Sea/Yellow Sea in the wake of Cheonan sinking. Even if the US did so after the artillery exchange in November 2010, it still didn't retaliate militarily against North Korea.

America mistakenly entered Iraq in 2003 under the pretext of Saddam's WMD build-up. However, Iran's persistent nuclear quest, regardless of various IAEA and UNSC warnings, has ridiculed any international pressures, including US deterrence. Israel is increasingly under pressure to launch a pre-emptive strike against Tehran so as not to burden US extended nuclear deterrence.

Beyond the seeming decline of extended nuclear deterrence, the aforementioned trend is also indicative of America's caution in wielding the nuclear option. What is at stake is not deterrence or extended deterrence, but security assurance per se. The US has actually not loosened its security commitment to its allies, but in order to maintain the credibility of its deterrent, America is now less willing to coerce its non-nuclear rivals while it has increasingly more non-nuclear tools in its policy kit. This was manifested in the Obama Administration's Nuclear Posture Review last year.

Both North Korea and Iran have understood this, to their benefit. Iran understands that its violation of various UNSC resolutions would at most incur a non-nuclear US response. Indeed, UN Secretary General Ban Ki-moon is mediating a nuclear swap arrangement to lessen international concern, which could legitimise Iran's uranium enrichment. North Korea has also ventured into crises short of inviting US military strikes, and it has presented its own conventional deterrence plus a looming nuclear deterrent. Deterrence is no longer a US gadget.

Mutual nuclear deterrence among major powers is indeed less relevant nowadays, in a globalising age. At a co-dependent time, there are more incentives for inter-state compromise and reconciliation, while contingencies which require a nuclear showdown are implausible — hence the decline of nuclear deterrence among major powers, and extended nuclear deterrence backed by various non-nuclear options.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user US Army Korea - IMCOM.

There is no reason to doubt American willingness to use nuclear forces against powers that cannot retaliate directly against the US, at least in relation to nuclear attacks when proportionality is not an issue. It is, for example, entirely credible that Washington would launch a nuclear attack against Pyongyang or Tehran if either of them used nuclear forces against a US ally, because neither have (for the time being) an assured capacity for nuclear retaliation against the US. 

But these are not the tough cases. The real question about the future of END is whether the US can credibly threaten nuclear attack against an adversary that could retaliate against the US – which for present purposes means Russia or China. 

Take Europe first. If Moscow launches a conventional invasion of a NATO ally – say Latvia or Estonia – could America credibly threaten nuclear attack to force Russia to withdraw? Could it persuade Moscow that the independence of the Baltic States is so important to America that it would accept nuclear attack on the US to preserve it? That seems to me very doubtful, because Russia today does not have the potential to dominate Eurasia the way it did in the Cold War. The stakes for America are simply not as high – and not high enough.

What of China? As General Xiong once asked, is Taiwan's independence worth Los Angeles? More broadly, is anything on the western side of the Pacific important enough to Washington to convince Beijing that America would accept nuclear attack on its homeland to defend it? Even Tokyo?

This is the core question for the future of END: what is so important to Americans today that they are willing to suffer nuclear attack to defend it? And can the US persuade friends and allies that it is willing to make this sacrifice? Many would suggest the maintenance of a US-led world order is important enough, but I doubt that, especially when the non-military challenges to that order are so strong anyway.

I think the costs of nuclear attack are so high that nothing except the defence of America's own territory and independence would justify them. In the Cold War, when it seemed one power could dominate Eurasia, America's own security appeared to be at risk from a Eurasian hegemon. Today, with at least two and maybe four major Eurasian powers, that risk seems very remote.

So against any power capable of delivering nuclear weapons onto American soil, END is an anachronism. Neither America not its allies yet accept this. The sooner they do the better for everyone.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user -Alina-.

It is also simply not true that NATO today is threatening nuclear retaliation for a Russian attack in the Baltics. Ever since the adoption of Flexible Response in 1968, NATO has deliberately developed the ability to respond conventionally against a major but limited Russian conventional attack. The 'threat that leaves something to chance' is still there, but NATO does not rely on it. 

And END has never been, and cannot be, a fail-proof panacea even against major war. Nevertheless, even a small reduction in the likelihood of major war would make it a valuable part of global and Asian security order.

In hindsight, the Cold War can easily seem more straightforward than it really was. Care is needed when using it as a quarry for arguments about future policies in Asia. The sources of US commitment to the defence of Europe, for example, were much more varied than is suggested by a purely realist perspective: a good case can be made that, from the late 1950s, outright conquest of Western Europe would have been a poisoned chalice for the Soviet Union. The willingness of the US to defend Europe even at the risk of nuclear attack on America rested not only on national interest, but also on common values, shared history and personal relationships. And extended deterrence was much stronger, and more credible, for it.

As long as the US remains a nuclear power, END will be an inseparable, even if implicit, part of its alliance relationships. And we do not see any US policy, or that of a major allies or potential adversary, indicating that the strength of the decades-old US alliance relationships in East Asia is fundamentally weakened. 

That is not to say that extended deterrence relationships do not evolve. But at a time of changing great power relativities, an increased attention to END in official circles is a sign of vitality, rather than of decline. As long as there was no prospect of a major threat, there was also no need for practical and visible nuclear cooperation. To us, the increasingly formalised dialogue about nuclear matters between the US and Japan and South Korea thus is a good sign of the continuing relevance of END in Asia. 

The debate about extended deterrence is as old as nuclear weapons themselves. As in the past, its intellectual attraction arises in large part from the tension between arguments about how the world should be in theory, and how it is in practice. At its core, END remains a leap of faith. But as long as all those decision-makers who matter are prepared to make that leap, END remains viable. And we see no empirical reason to doubt that this will not, for the foreseeable future, be the case for American END in East Asia.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

This prospect worried De Gaulle and, like Hugh, he publicly doubted END and so France developed — admittedly for many other reasons as well — a nuclear force and a nuclear technology base. But other European nations were both more sanguine and the receipts of American generosity. The Eisenhower Administration embraced nuclear sharing and several European countries became able to deliver loaned US nuclear weapons, albeit with a dual key.

This was a powerful rebuttal to those who doubted END, and sowed more seeds of uncertainty. If Bonn was vaporized would the Americans allow the West Germans to head east? And not just that; could America in the confusion stop them even if it wanted to? Would you risk Kiev on it?

At the end, END lives because nuclear weapons are really, really scary and so even little risks loom very large in decision-makers' minds, encouraging them towards caution. But the Cold War was very dangerous; the American military wanted to invade Cuba in 1962, not realising that nuclear weapons were already in Cuba awaiting them, while the Soviets got confused over Able Archer 83 and considered a pre-emptive attack in Reagan's first term.

Today though in the nuclear stakes, its hard to get past Pakistan, a Chinese and American ally that keeps building bombs while it gratefully accepts foreign aid. The New York Times reported last week that Pakistan is now the fifth largest nuclear power, surpassing the UK and will soon pass France, the fourth. Numbers are not yields, and this measure may not be as important as might be thought, but Pakistan's nuclear ambitions will keep many thinking and worrying about where this all END(s).

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

It could indeed be argued that Pyongyang was testing the limits of US protection to Seoul. However, another intriguing possibility should be raised: that North Korea was very careful to strike a 'disputed' area, one which was – at least from its point of view – not part of the territory covered by the US umbrella. In so doing, it may have acted like Egypt and Syria did in 1973: facing a nuclear-armed adversary, they were very careful not to attack Israel on its 1948 borders.

Hugh White raises an extremely important question: he wonders if Washington would threaten nuclear war for the sake of the Baltic states, since the risk of 'losing Europe' would be limited. In other words, the stakes would be much lower than during the Cold War. But, as in most discussions about deterrence, one has to consider the problem the other way round: would Moscow take the risk of invading the Baltic states, given that it would face three nuclear-armed adversaries and risk a military escalation that could, ultimately, end up in a nuclear exchange?

My answer is 'no'. It may be precisely because Georgia was not under NATO or US protection that Russia considered it could take a chance in 2008. (Incidentally, here again we see an intervention on what was arguably a disputed area: the Abkhazian and South Ossetian territories. Western reaction could very well be what stopped Moscow from going further.) 

White also quotes with appreciation the reported 1996 statement by a Chinese official, according to which the US cares more about Los Angeles than it does about Taiwan. However, during a crisis in the Taiwan straits, the 'deterrence dialogue' would not stop there. The question is: what would Washington tell Beijing if China threatened to escalate the conflict to the US homeland? My guess: the US president would say 'try me'.

In other words, the credibility of the US extended deterrence to Taiwan depends not on the relative values of Taiwan and Los Angeles for Washington, but on the respective beliefs of Chinese and American officials about the sequence of a US-China nuclear war. A classic deterrence issue.

Shen Dingli makes a different but related point when he states that globalisation and interdependence have made nuclear deterrence among major powers less relevant than it used to be. That may be true, and there is something like a 'financial balance of terror' between Washington and Beijing. But I would caution against definitive conclusions: the First World War erupted at a time of (then) unprecedented economic interdependence between the major European powers of the time. This did not trump political passions and the strength of ideologies.

UPDATE: I described in an earlier post the 1950 North Korean attack as a 'failure of extended deterrence'. I should clarify what I meant. There was no formal extended deterrence to South Korea at that time. But by stating that the Korean peninsula was not part of the defensive perimeter of the US, Washington signaled explicitly to North Korea and its allies the absence of such a deterrent and gave a green light to the invasion.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user The US Army.

With the withdrawal of US nuclear weapons from South Korea in 1991, there are no US nuclear weapons forward deployed in the Asia Pacific. Instead, American officials have largely pointed to specific capabilities in the American arsenal that are said to be maintained for the unique task of extend deterrence, on the grounds that if we are willing to spend money, we must be serious.

So, for example, in 2001, the Bush Administration told Japan that the US was retaining the option to deploy nuclear-armed Tomahawk missiles (which were sitting in storage) on US attack submarines just to show we were serious about defending Japan.

The problem with this approach is that US conventional and nuclear capabilities continue to evolve – relying on hardware commits us to those capabilities long past their obsolescence. The US would not, under any conceivable circumstance, have redeployed the nuclear Tomahawk. All along, the Navy intended to retire the system in 2013.

In 2010, the Obama Administration had to choose between explaining to Tokyo that, perhaps, American officials hadn't been entirely truthful in 2002 and the system would be retired, or spending money the Navy didn't have to maintain the system in storage. Fortunately, the Obama Administration decided to proceed with the retirement of the nuclear Tomahawk. The Administration calculated, correctly, that consultations were much more important than the nuclear Tomahawk. 

Unfortunately, the 2010 Nuclear Posture Review also continued the short-sighted practice of pointing to one shiny piece of hardware to replace another. This time, the US asserted that its commitment to extended deterrence was demonstrated by the effort to make nuclear-capable the Joint Strike Fighter (and extend the life of the B61 nuclear gravity bomb it would carry) and maintain the capability to forward deploy US bombers, like the B2, particularly in Guam.

These are, however, irrelevant capabilities that may not survive the current budget austerity. There are no military missions for the B61s deployed in Europe – one NATO official admitted to me that 'we would never drop a B61 off the wing of an airplane' – and the Air Force does not want to spend money giving the JSF an obsolete nuclear capability (nor do our European partners seem keen to modernise their own 'dual capable' aircraft).

Nor would the US forward deploy nuclear-armed B2s, either to Guam or elsewhere (conventionally-armed bombers are another matter). The B2 can reach targets from North Korea to Iran directly from Missouri, which is what the US did in the early stages of operations against Yugoslavia, Afghanistan and Iraq.

Either this Administration or the next is going to end up explaining that the 2010 Nuclear Posture Review, in its own way, was not entirely truthful.

Perhaps the solution is to stop talking about extended deterrence as though it were a separate mission. Instead, we should talk about core deterrence – the central mission of nuclear weapons to deter nuclear attacks against the US, our forces abroad and our allies and partners. One advantage to talking about core deterrence is that it forces us to set aside the hardware and focus on the real question: how do we demonstrate that an ally is part of the core?

On the narrow subject of nuclear weapons, this means emphasising consultation and joint planning that binds countries together. But more broadly, changing our language reflects the reality that the credibility of the 'nuclear umbrella' is really just a manifestation of the credibility of our shared interests and values. Forging an alliance on this basis isn't quite as easy as pointing to shiny new piece of hardware, of course, but it is likely to endure long after this bomb or that missile has gone to rust.

 

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

 

Photo by Flickr user solidether.

Although the role of nuclear weapons in extended deterrence will not vanish, other elements of deterrence and extended deterrence are increasingly important to maintain credibility by assuring allies and adversaries in various crisis scenarios. Since the role of deterrence is to reduce the risk of conventional aggression as well as nuclear exchange, extended deterrence should pursue the best mix of nuclear, non-nuclear (conventional) forces and political means.

Furthermore, as Shen Dingli points out, there are various interpretations of the effectiveness of extended nuclear deterrence. It indicates that the perception element among three elements of credible extended nuclear deterrence needs to be further considered.

Second, asymmetry between the US and China in force structure and strategic objectives makes it complicated to establish strategic stability in East Asia. While US strategic forces shift towards long-range strategic nukes, the majority of Chinese nuclear forces remain short- and medium-range (although China has been developing its long-range capabilities). US arms control policy values a balance of forces as well as transparency and verification, while China puts more emphasis on confidence building measures such as no-first-use and the negative security assurance, both of which are difficult to verify.

During the Cold War, strategic stability between the US and Russia converged into a balance in the number of strategic nuclear weapons, and was consolidated through arms control treaties by the concept of mutually assured destruction. Two countries developed transparency and verification measures to maintain strategic stability. In such a relationship, the US and Russia admitted that they were both in a mutually vulnerable situation, and mutually confirmed a kind of 'pro forma' standardised strategic stability.

In a time when we are experiencing a paradigm shift regarding the role of nuclear weapons in international security and relationships among nuclear armed states, traditional nuclear deterrence logic that was built upon the history of the US-Soviet (Russian) confrontation does not necessarily guarantee the legitimacy of nuclear weapons or nuclear deterrence. Rather, the necessity of structuring a new logic of 'strategic stability' is rising. There is a need for strategic dialogue to converge different arms control philosophies into a shared vision, involving both nuclear weapons states and their allies.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user m'sieur rico.

This policy creates cynicism towards the NPT; an increasing belief that, far from being a road map to a nuclear free world, it is a document enshrining nuclear weapons as a God-given right for some, but which no one else has any right to acquire. This status quo, along with the END argument that underpins it, is wholly unsustainable.

The NPT is further undermined by double standards toward those (such as India) existing outside the NPT but who have nevertheless become treated as NPT nuclear weapons states, minus any of the responsibilities or obligations that come with it.

The existence of END damages nuclear disarmament directly by providing cover for other nuclear armed states. Russia remains largely free of criticism so long as it maintains parity reductions with the US. Other nuclear powers claim they will participate in multilateral reductions once the two Cold War arsenals are reduced closer to minimum deterrence levels, but since this cannot happen while END exists, they get a free ride.

The US believes its revised negative security assurance reassures non-nuclear states while maintaining nuclear deterrence against perceived proliferators. This is nonsense. In no way does the revised negative security assurance have this effect, and in some important ways it causes considerable harm. Short of a country being a launch site for a nuclear attack, there is no scenario in which the US would conduct a nuclear strike against a non-nuclear weapons state; the assurance that it will not do so is simply stating the obvious.

Also, the overt exclusion of Iran and North Korea from the negative security assurance is a serious error. Everyone knows that the US is never going to launch a pre-emptive nuclear strike on either country, so the only practical effect of the revised assurance is to lend legitimacy to the Iranian and North Korean nuclear programs. Surely if there is one legitimate reason for acquiring nuclear weapons, it is somebody openly threatening to use them against you.

The nuclear taboo that constrains nuclear powers and limits the utility of nuclear weapons holds similar implications for END. Since no state actor can achieve desired foreign policy goals by nuking non-nuclear weapon states, END is unnecessary. Its removal would assist disarmament efforts and strengthen the nuclear taboo even further.

It is also the case that non-nuclear weapon states are seldom deterred or successfully blackmailed by another's nuclear arsenal. Argentina was not deterred by Britain's nuclear weapons in the Falklands, and China was not deterred by America's nuclear weapons in Korea. In the aftermath of the Second World War, the Truman Administration was perpetually dismayed by just how unfazed the Soviet Union was by America's global nuclear monopoly; the Soviet Union continued to maintain all of its political demands and even blockaded Berlin.

END is a self-serving policy with little, if any, benefit to the common strategic good. It is saddled with many drawbacks, in particular providing political cover for major nuclear powers and undermining nuclear disarmament efforts.

The argument that other countries will acquire nuclear weapons without END is unpersuasive. By far the greatest constraint on horizontal proliferation is the NPT, and its continued degradation, in part due to END, is one of the biggest threats to nuclear disarmament worldwide.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user windy_sydney

As Bruno Tertrais suggests, it is inconceivable that an adversary, if rational, would fail to consider the possibility of US nuclear retaliation, however remote it is from the US, and even if it possesses a reliable second strike capability, when it comes to conducting even a limited military option against Japan.

Of course, we should not place exaggerated hopes on END, as US allies such as Japan have occasionally done. Even if the US maintains a robust defense commitment, including the provision of END, an adversary may conduct a low-intensity military option under deliberate consideration, or by miscalculation, misperception, overestimation of its capabilities, or even underestimation of US resolve. END is not a panacea, and we need to keep contemplating the roles and limits of END in a realistic manner.

END is indeed significant, but it is just one of various means for guaranteeing an ally's security and mitigating threats. Rather than just relying on END, it is imperative for Japan to reinforce its efforts, under close coordination and cooperation with the US, to construct stronger conventional capabilities — including addressing anti-access or area denial capabilities, developing missile defense and sharing roles, burdens and capabilities — for adequately deterring the low-intensity, limited challenges that Japan may face, as well as denying an adversary's escalation or achievement of objectives.

Such efforts will contribute to further enhancing Japan's own deterrent capability, the Japan-US alliance, and the credibility of US END.

Finally, END will become less and less imperative where military challenges or threat have been mitigated or have vanished. In achieving this goal, the importance of enduring efforts toward deepening strategic dialogues, developing transparency and confidence building measures, creating a communication mechanism in case tension heightens, and promoting arms control and non-proliferation are steadily but surely increasing in Northeast Asia.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user Ciro@Tokyo

What I mean by 'sincere' is not just verbal promises but real action by the US. After the first North Korean nuclear test in 2006, more than 67% of South Koreans approved the idea of developing South Korea's own nuclear weapons. With the imminent threat of North Korea, South Korea did not feel secure with the provision of extended nuclear deterrence from the US, which is so remote from South Korea. So the problem does not lie in whether extended nuclear deterrence is needed or not, but whether extended nuclear deterrence can be provided in assured and valid ways.

The second argument for extended nuclear deterrence concerns the credibility of deterring North Korea. The probability that the North would actually use nuclear weapons is very minimal, and most of the skirmishes in the Korean peninsula are limited to the small-scale aggressions like the Cheonan ship sinking and Yeonpyong island military attack. In this vein, George Perkovich argued that the role of non-nuclear deterrence is significant. But still, in this case, the role of nuclear deterrence cannot be ignored.

Recent North Korean military provocations prove that US extended deterrence has failed. Despite ongoing US promulgations of its solid extended deterrence provision to South Korea, North Korea has continued its military provocations because the North knows that the US would not willing to retaliate: the US does not want small skirmishes to be escalated into a large-scale warfare. This implies that the US and South Korea are deterred by the North.

This stalemate necessitates the role of nuclear weapons. All the partners within and surrounding the Korean peninsula are well aware that the risk of using nuclear weapons is very minimal. But it is more about psychological effect and a game of bluff. It is such a game of bluff that made North Korea restless when the US nuclear-powered aircraft carrier George Washington participated in the US-South Korea military exercises near North Korea. Actual use of nuclear weapons is unlikely, but it still retains a psychological deterrent effect.

Cold War strategic stability was maintained by the nuclear strategies of the US and Soviet Union based upon their virtual use of nuclear weapons. Now, it rests more on psychological, if not symbolic, effect.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user US Army Korea - IMCOM.

There are a number of reasons to be pessimistic. To begin with, Australia's nuclear dilemma reflects a broader problem in its alliance relations with the US, which I've explored elsewhere. The dual risks of abandonment and entrapment, common to all alliances, sharpen as the distribution of world power shifts, with important implications for the credibility of America's nuclear umbrella.

The risks of entrapment arise in two forms. At a general level, Canberra's strategic dependence on Washington, including for END, circumscribes its ability to dissent from American policies that may not accord with Australian interests. Cognisant of its privileged place under the US nuclear umbrella — and of its limited range of alternatives, should END be withdrawn in the event of Australian non-compliance (a la New Zealand circa 1984-1987) — Canberra could find itself dragged into a costly war alongside the US that its fortuitous strategic geography might otherwise allow it to avoid.

More directly, the joint facilities that Australia hosts as a quid-pro-quo for US nuclear assurances — critical as they are to America's intelligence, surveillance and reconnaissance network — could present as valuable targets in major war that, by virtue of their distance from Northeast Asia, only nuclear-tipped ICBMs may be reliably assured of destroying.

This may sound rather fantastic, yet it's not a consideration that Australian defence planners can automatically discount. Moreover, there is a historical basis to such concerns. As former defence minister Kim Beazley once noted in the context of the Cold War, 'we accepted that the joint facilities were probably targets, but we accepted the risk of that for what we saw as the benefits of global stability.'

These concerns notwithstanding, it is the risks associated with abandonment that are the most acute. Credible nuclear deterrence operates on the basis of a defending state's threat — through some combination of explicit pronouncements and the deployment of nuclear capabilities — to impose intolerable costs on an attacker, thereby preventing the attacker from using nuclear weapons against the defender's ally. By contrast to conventional deterrence, where risks are generally limited, nuclear deterrence relies on the defender — in this case, the US — conveying a willingness to sacrifice large swathes of its population on behalf of Australia, which is an essentially non-vital, possibly even marginal, strategic interest. The question for Australian defence planners is: would the US government really trade San Francisco for Sydney?

Indeed, if Canberra's broader quest for self-reliance reflects enduring concerns about the potential limits of Washington's willingness or ability to furnish assistance in a strategic crisis, there is no compelling logical reason why, with the balance of power shifting away from US primacy, those concerns should be so sharply limited to conventional threats. If anything, Australian defence planners should expect Washington to act with greater caution and more reticence in a nuclear crisis, however unlikely one might be, when the costs and risks to itself will inevitably be exponentially greater.

I ventured a few thoughts on how Australia might begin redressing its nuclear dilemma in this article a few years ago. Unfortunately, however, the traditional impetus for change in Australian strategic policy is crisis, or at least perceptions of crisis, at which point it's usually too late to do anything other than 'muddle through'. This is likely to be doubly true of nuclear issues, which, given the wide-spread aversion to even discussing them in Australia, remain largely beyond the realm of acceptable political discourse. So don't expect any movement for at least a couple of decades. 

In the meantime, is END dead? Let's hope we never have to find out.

This is a much commended, progressive nuclear policy, reducing the role of nuclear weapons in international politics. There is a dilemma: the more the US stresses deterrence and extended deterrence, the more its allies could feel assured and less likely to pursue their own nukes, but the more likely some other countries would feel the importance of nuclear weapons and their associated deterrence and therefore seek their own nuclear path. Everyone has to weigh the balance between security due to the nuclear umbrella and insecurity due to nuclear proliferation.

Obama's policy has obviously reduced the role of nuclear weapons in America's national security, so as to create a situation more conducive to nonproliferation. Obviously this has an impact on extended nuclear deterrence — the US now is clear that it would not protect its allies with nuclear weapons against non-nuclear attack, possibly with Iran as an exception. Its current nuclear doctrine has deviated from traditional extended nuclear deterrence — if an aforementioned non-nuclear state rival now brings harm to America or its ally, as long as it is in good standing with the NPT, the US has promised not to retaliate with nuclear weapons.

This may sound frustrating to some but one has to remember that every coin has two sides – America wants to bring more security to itself and its allies in an age of proliferation. It has to commit less to its nuclear umbrella and to its friends, though it could still assure its allies through other means in the future.

Whether one likes such a change or not, this is the Obama position. So how we can say nuclear extended deterrence has not declined?

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user x-ray delta one. 

Now consider America's most important ally today. END is not a free good for Japan. Preserving END costs Japan the option of developing its own nuclear forces. The future of END for Japan depends not simply on whether Japan believes it benefits from America's promise, but whether it believes accepting END provides Japan with more security than the alternative. This is a pressing question for Japan today, not just because its fears of China are growing, but because Tokyo's confidence that America's promises will stick are fading.

The reason is that END carries costs to the US as well. As I said in my earlier post, these costs are low when the adversary cannot retaliate against the US. But against an adversary capable of nuclear attack on American soil, the costs are considerable. It is easy to underestimate the costs of END imposed by the risk of retaliation if we discount the risk that a crisis involving a US ally would escalate to a nuclear exchange. But should we do that?

To explore this we need to look quickly at the relationship between END and its close cousin, Extended Conventional Deterrence (ECD). Several posts in this debate have touched on the connection between END and ECD, but I'm not sure we are clear about it. At first glance it seems simple enough: in both cases the US promises to protect its allies, and the only difference is the kind of forces it is prepared to use. Much is made of the effectiveness of conventional US forces to protect allies, which carries the optimistic implication that the costs to the US of this kind of extended deterrence are low. Indeed optimists about the durability of END tend to blur the distinction between END and ECD, viewing them as two sides of the same coin and suggesting that END is really not much more risky than ECD for the US.

I do not agree with this. First, how distinct are ECD and END in practice? Much depends on the context. It is easy to exclude the possibility of nuclear use by the US against a non-nuclear adversary that does not have clear conventional superiority. But against an adversary which has either the capacity to prevail against US and allied conventional forces, or has nuclear weapons, or both, then excluding a nuclear response would drastically weaken the value of US promises of support. So against these adversaries — the ones that matter, in other words — any extended deterrence must be nuclear to be effective. 

Second, the threshold at which the nuclear element of extended deterrence comes into play in a crisis would be much lower than people may think. Several posts in this debate — Stephan and Ben's talking about the Baltics, for example — seem to suggest that the US could respond to conventional threats with conventional forces, and hence fulfill its promises to allies, without running the risks of nuclear war. This is because the threat of US nuclear retaliation would deter the Russians from threatening nuclear action in response to US conventional operations. 

My hunch is that, on the contrary, there is a real risk of escalation to a nuclear exchange in any conventional clash between two nuclear powers, as long as there is asymmetry in their calculations of cost and risk. In particular, geography imposes structural asymmetries of interest between the US and its Eurasian competitors which would profoundly affect calculations in a crisis.

For example, in a crisis between the US and Russia over a Baltic state, the risks might be symmetrical but interests are not. The Baltics matter a lot more to Russia than they do to America. This does not mean Russia would be prepared to accept a nuclear attack to get hold of Estonia (for example). But it does mean Moscow would probably calculate that the US would not be willing to risk nuclear attack to save Estonia. So, assuming the Russians believed they could prevail in a conventional attack on Estonia, they might well calculate that the US would not be willing to escalate from conventional to nuclear warfare to stop them. And the Estonians might well think so too. 

Now back to Japan. It is entirely credible that the US would retaliate with nuclear forces to any direct nuclear attack on Japan, so this element of END remains intact. But that is not enough for Japan to feel secure, especially from China, because it leaves open the credibility of US undertakings in the event of a conventional crisis.

Consider a Chinese conventional attack on Japan's Ryuku Islands. America's formidable sea-denial capability would be able to interdict Chinese sea-borne forces, but China could threaten substantial conventional retaliation against US interests, so the costs to the US of supporting Japan in this situation would be very high. The question would arise whether the Ryukus were worth it. But say firmness prevailed in Washington, and the Air-Sea Battle swung into action. China might then threaten nuclear escalation if the US persisted — initially perhaps against Guam.

America would of course threaten nuclear retaliation against China. But while the risks are broadly symmetrical, the interests are not: China cares more about the Ryukus that the US does. It is the Cuban Missile Crisis in reverse. So American decision-makers might well decide that China's threats must be taken seriously. They would then ask themselves whether the Ryukus are worth LA, just as General Xiong suggested. The answer is not a forgone conclusion.

This is very important for Japanese decision-makers weighing the costs and risks of different options for Japan over the next decade or two. Going nuclear would carry huge costs for Japan, but relying on END carries big risks.    

END evolved during the specific circumstances of the Cold War when, for reasons I sketched in my earlier post, American interests in Europe and Asia were as great as those of the Europeans and Asians themselves. Today this is no longer true, because neither China nor Russia today poses the kind of threat to America that the Soviets once posed. It is this widening asymmetry of interest between America and its Eurasian allies that undermines END.           

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute  

 Photo by Flickr user discoodoni

Deterrence on the Korean Peninsula is even more complicated because it works in different ways at different levels. The full spectrum of US and ROK power deters a full-scale invasion by North Korea. But the DPRK's forward-deployed conventional forces and their capacity to wreak extensive damage in the densely populated Seoul metropolitan area have generally led Seoul and Washington to be very cautious about using conventional force against the North. Pyongyang, therefore, has seen only modest risk in undertaking provocative military actions against the South, such as the sinking of the ROK Navy's Cheonan in March 2010 and the shelling of Yeonpyeong Island eight months later. (For an excellent discussion of these issues, see this essay by Admiral (Ret.) Mike McDevitt).

One reason Pyongyang has taken these reckless actions, it seems, is a belief that China is willing to tolerate them. At both levels, the situation is now taking a serious turn. In order to promote both deterrence and domestic solidarity, Seoul has decided that it will retaliate 'kinetically' against future DPRK conventional provocations. That, of course, raises the danger that North Korea will not simply absorb the punishment but retaliate itself. Controlling escalation would become a serious challenge. The chances increase that the US and China — the backers of the two Koreas — would become parties to a widening conflict. What is their stomach for a fight? What is their stomach for not fighting and bearing the costs of backing down?

At the strategic level, it appears to be only a matter of time before the DPRK is able to hit the continental US with a nuclear weapon. In January, in Beijing, Defense Secretary Robert Gates said, 'With the North Koreans' continuing development of nuclear weapons, and their development of intercontinental ballistic missiles, North Korea is becoming a direct threat to the United States'.

Which raises the question, would the US be willing to lose San Francisco as a price for protecting Seoul? Would the government and people of South Korea and the regime in Pyongyang believe Washington would make that sacrifice? Based on what facts and logic would they make that judgment? If they are not convinced, will they opt for their own nuclear deterrent? (A recent poll suggested that the South Korean public is split down the middle on a nuclear option.)

To strengthen deterrence, Washington and Seoul are employing a 'bank shot'. They seek to persuade China that it is not in its interests to allow North Korea to define the security environment in Northeast Asia, either at the level of conventional provocations (with the danger of escalation) or at the strategic level (with the prospect of regional destabilisation). Beijing, of course, is not able to dictate Pyongyang's security policy, but it does have points of influence: the degree of its support for the succession to Kim Jong-il, whether it constrains vital North Korean trade that flows through China, and so on. Moreover, it cannot idly ignore the consequences for China's national security as a result of the measures that the ROK and the US take to strengthen deterrence.

That is the leverage that Seoul and Washington now seek to exercise, with the hope that China will restrain its North Korean partner, not as a favour to them but to better secure China. If successful, this effort will help guarantee that American extended deterrence pledges will never have to be honoured.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo, of a North Korean guard looking south, courtesy of the US Army Korea IMCOM

A war on the Korean Peninsula, would not put at risk the existence of the US, even if Pyongyang were to field an ICBM; it would, however, jeopardize Kim Jong-il's regime and the North Korean state.

Nor would a nuclear Iran pose an existential threat to the US. Tehran's clerics could, however, judge that a war with the US could lead to their ouster. Washington's opponents thus have a strong motivation to escalate future conflicts. 

Fourth, technology has changed the nuclear landscape, blurring traditional distinctions between conventional and nuclear arms. Whereas commentators on the left have for years feared that fielding more discriminate nuclear weapons would 'conventionalise' them, in fact conventional arms now approach the effectiveness of nuclear weapons.

Soviet military theorists writing in the late 1970s were among the first to observe that precision-guided munitions (PGMs) were being fielded with an effectiveness nearing that of small tactical-nuclear-weapons. 

Conventional PGMs are today capable of destroying a wide range of targets that until recently would have required nuclear weapons. In addition, the deployment of ballistic missile defenses now offers the prospect of defending the US, our forces, and our allies against missile attack.

The changed nuclear environment, in turn, suggests that nuclear weapons could be employed in a broader set of circumstances than in the past. The recently published report of the Johns Hopkins University, Nuclear Futures Project, explores some of these scenarios. They include nuclear use arising out of the implosion of North Korea, a conflict across the Taiwan Strait, a failed Israeli pre-emptive strike against a nuclear Iran, the collapse of Pakistan, or a terrorist attack on the US.

A number of these plausible scenarios could call into question US END guarantees. A conflict with North Korea or China, and prospectively with a nuclear Iran, could escalate to involve nuclear strikes on US bases in allied territory, or even (in the case of China) on sovereign US territory such as Guam. 

A nuclear strike on Japan arising out of the collapse of the regime in Pyongyang or a conflict across the Taiwan Strait, would lay bare the dilemma that underpins END: extending nuclear guarantees is meant to lessen the pressure on an ally to acquire nuclear weapons, but in so doing, the US puts at risk its own security on behalf of an ally. 

According to the US-Japan Defense Treaty, Washington is committed to the defense of Japan; to not do so would mark the end of the alliance. However, a retaliatory strike would invite further nuclear attacks on Japan and potentially against the United States.

In other cases, it is possible to envision other states seeking END guarantees. Should Iran go nuclear, other states in the Gulf region might seek END guarantees from the US. The Gulf Cooperation Council states, would be increasingly vulnerable to Iranian coercion. Iraq, an Arab state with a Shi'a majority on Iran's borders, would be particularly uncomfortable in Iran's nuclear shadow.

Compounding the challenge of the US maintaining END, is its decreasing means of doing so. The US has traditionally underwritten its END guarantees with forward-based forces. However, Washington has decreased markedly the size of its theater nuclear forces since the end of the Cold War. According to the Pentagon, the number of non-strategic US nuclear warheads declined by approximately 90% from 1991 to 2009.

If END is to endure, then the US and its allies will need to work harder at maintaining and bolstering it. This may include declaratory policy, but will also likely require changes in force posture to increase the credibility of extended deterrence. This debate is a good way to foster such a dialogue. 

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo, of a US Air Force B-2 Spirit and two B-117A Nighthawks, by Flickr user mashleymorgan.

Where threat perceptions align as closely as they did for the US and Europe during the Cold War, END was more effective as it offered the Soviets few gaps to exploit. Fast forward to 2010, and we see the North Koreans exploiting a gap in shelling Yeonpyeong Island.

North Korea knew the attack would harm South Korea, but that a US military response would be very unlikely. While the South Korean Defence Minister initially mooted the redeployment of tactical nuclear weapons on the Peninsula (he lost his job soon after), the US responded by sending a carrier into the Yellow Sea for military exercises. From either country's perspective, the other reacted disproportionately, just as the North Koreans would have anticipated.

If such differences emerge between provider and beneficiary that an adversary can poke holes in both the nuclear umbrella specifically and extended deterrence more broadly, how can END be anything but an abject failure, as Hyun-Wook Kim concluded? This question touches on a number of strategic dilemmas.

One of these is how we judge whether extended deterrence succeeds — is it only where the beneficiary is fully satisfied with the result, or can it succeed where the result is some sort of compromise? How does a concept such as deterrence, which requires mutual understanding, function where it involves three countries with three different perceptions of interest.

Should extended deterrence respond to 'sabre rattling' or be reserved for major threats? There are no right or wrong answers to these dilemmas, but the choice of answer determines whether one sees events like Yeonpyeong as failures, or symptomatic of the limited, imprecise but still functional nature of END.

Two brief arguments in favour of extended deterrence can be drawn out of these dilemmas, though in the Korean case they moderated rather than prevented the 'failure' (from a South Korean perspective) of extended deterrence:

First, if the alliance relationship creates an opportunity to negotiate a response that is satisfactory in both parties' opinions, bringing their calculations of proportionality closer together, then it is a plus for regional security. While the real test of this will come when the US-ROK Extended Deterrence Policy Committee has had time to work out how certain North Korean contingencies will be met, avoiding some of the more assertive options mooted in Seoul last October likely saved a fair few Korean lives.

Second, as a provider of END to multiple countries, Washington's actions are closely monitored by both allies and adversaries the world over. Maintaining its credibility to others would play no small role in its calculations of a proportionate response, giving the beneficiary of extended deterrence more clout in negotiating a response than it would otherwise have.

But two other arguments weigh in heavily against extended deterrence: First, as the Korean Peninsula situation illustrates, nuclear deterrence is usually irrelevant to crisis situations that invoke the alliance. At times, any military response at all is inappropriate, even if it would be proportionate, because of the specific risks it would create in such volatile circumstances.

Second, the likelihood of an extended deterrence failure is even higher if the provider is on an adversary's nuclear targeting list. Proportionality calculations are suddenly muddied by the desire to avoid bringing the conflict home.

Tom Mahnken and Duncan Brown seem to suggest that the US would suffer but ultimately prevail in a conflict with an adversary who could deliver nuclear weapons to US soil, an argument somewhat reminiscent of Mao's comments about China's ability to absorb a nuclear attack.

I am sceptical that a president of a democracy would take such a clinical approach to the lives of large numbers of citizens in an extended deterrence situation. Risking the blood of your citizens to protect or retaliate on behalf of your ally is an exceptionally high stakes game that is difficult to imagine today, but may well arise in the future. For example across the Taiwan Straits.

In these situations, trying to calculate a proportionate response soon reveals why END can be both a terrific success and a disastrous failure. The hard cases all depend on whether individual decision-makers are willing to let their fingers hover over the red button, and whether they think their adversary is equally willing.

Prudence dictates that we treat END as alive and well. Doing so will reduce the risk that it will ever need to be tested.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user gravity_grave.

Bruno Tertrais notes the non-proliferation benefits of END and argues that it is alive and changing. But he also acknowledges that a greater reliance on non-nuclear forces need not make extended deterrence less credible. Having a range of non-nuclear capabilities might prevent the wielder of the nuclear umbrella being self-deterred by a brutal choice between all-out nuclear war or backing down.

Interestingly, despite his general advocacy of END, Tertrais recognises it as relying more on the psychology of leaders than the proximity of weapons — an argument against those, for instance in Europe or South Korea, who support tactical nuclear deployments.

Shen Dingli argues that recent trends and events suggest that END is moving towards irrelevance. He suggests that events in Northern Asia in 2010, the sinking of the Cheonan and the shelling of Yeonpyeong island, amount to a failure of END. Yet, as others such as Nobu Akiyama argue, this could simply be the stability-instability paradox in action.

In a sense, these events might even show END as working: after all, both Seoul and Washington tempered their responses with a clear sense of proportionality. And, as some other contributors note, the various consultative dialogues on END involving Washington, Seoul and Tokyo could be a sign of its stable adaptation.

The vital ingredient of proportionality informs the views of many other contributors, notably Hugh White and Fiona Cunningham. But they reach rather different conclusions. White asks whether the United States really would use nuclear weapons to defend an ally in circumstances where a nuclear adversary could strike American territory, and moreover where critical American interests were not at stake.

This leads him to conclude that in most circumstances END is becoming an anachronism. He does not say much about what might take its place, although his second post suggests reasons why an ally like Japan might come to want nuclear weapons of its own. This point is alluded to by Raoul Heinrichs, who also offers a view on the Australian context.

Stephan Fruehling, Benjamin Schreer and, in his second post Tertrais, remind us that the psychology of the prospective adversary is at least as important as that of the nation wielding the nuclear umbrella, or indeed of its threatened ally. For this reason, they argue, END remains likely to reduce the risk of war.

One issue that was not explored at depth in the debate, yet which cannot be overlooked, is whether the potentially catastrophic consequences of nuclear escalation are worth that reduced likelihood of conflict.

Jeffrey Lewis grabs our attention by proclaiming there is no such thing as the nuclear umbrella; even as a metaphor, it would seem, this term can be misleading. There are alliances, he says, and there are nuclear weapons, but the link between them is an inference, albeit reasonable. From here, he argues that the credibility of END should be linked, not to numbers or forward deployed capabilities, but to the strength of alliences — consultation and joint planning, as well as their shared interests and values. 

Such ideas may remain difficult to sell in some parts of Seoul and Tokyo. Hyun-Wook Kim argues that END remains important and generally effective, and refers to the prominent calls in South Korea for the return of US tactical nuclear weapons to the peninsula. However, he also asserts that the Cheonan and Yeonpyeong attacks by North Korea prove that US extended deterrence has failed.

These events feature widely in our debate, but their meaning remains contested. Kim sees them as a reason for more deterrence; Shen as reason for less.

Japanese experts Nobu Akiyama and Hirofumi Tosaki both point broadly to the continued relevance of END, but also to its limits. They focus on how the Asian threat environment is changing, and how the US and its allies thus need to strengthen their non-nuclear deterrent capabilities.

They also suggests a need to look for a new basis of strategic stability, notably between the US and China, with a role for diplomacy and confidence-building measures in reducing mutual threat perceptions. Richard Bush takes this point further, emphasizing the need to persuade Beijing that restraining North Korea's nuclear weapons ambitions and belligerent behaviour is in China's interests. Such a move would reduce the need for the US, South Korea and Japan to strengthen their capabilities and alliances.

One striking thread throughout the discussion, is how much psychology and perception will matter in determining whether the nuclear umbrella or, if one prefers, an inclusive form of core deterrence, can weather the strategic turbulence that may well lie ahead. In the end as Fiona Cunningham and several other contributors imply, it could be an act of choice — an open affirmation of belief in END — that helps reduce the likelihood that it will ever need to be tested.

Extended nuclear deterrence is not dead. But, to paraphrase a great Italian novelist, for its positive effects to stay the same, it will have to change. As global efforts to reduce nuclear dangers continue, END will inevitably be examined as a source both of stability and possibly less desirable effects.

Moreover, nations that consider themselves protected by US nuclear guarantees, have to address questions about their own credibility as advocates of nuclear non-proliferation and disarmament. In a world of diverse and changing threats, their continued embrace of END is understandable. But they would do well to consider how END might most safely be refined for 21st century circumstances.

For a start, this might involve allies agreeing that a practical and moral nuclear umbrella can function only against existential threats, along with their renewed willingness to contribute more towards non-nuclear defence.

The Nuclear Reactions column is supported by the Nuclear Security Project of the Nuclear Threat Initiative, as part of a wider partnership between the NSP and the Lowy Institute.

Photo by Flickr user jordi.martorell.