Dr Stephan Frühling and Dr Benjamin Schreer are Lecturer and Senior Lecturer in the Strategic and Defence Studies Centre, ANU.

Previous entries in The Interpreter's debate on the future of extended nuclear deterrence (END) make a valuable contribution to the discussion about this important aspect of Asian security order. Both Hugh White and Shen Dingli see US willingness and ability to provide assurance to its allies as being in decline. 

Hugh's deliberate mirror-imaging follows an established approach to the theory on deterrence. There is a long tradition of analysts using it to argue for their policy prescriptions, not least Nobel-prize winning Thomas Schelling. 

But as Bruno Tertrais points out, deterrence is a psychological phenomenon. Therefore, judgements about its viability must ultimately rest on empirical evidence of real-life attitudes and policies. And to us, the evidence points to a more positive view of the viability of US END in East Asia.

We must be careful not to ascribe to END a greater remit than it really has. George Perkovich remarks that END is only suited to dealing with the possibility of a major, existential threat. Skirmishes on the Korean Peninsula are nothing new, and no argument that END, or even extended deterrence in general, is failing. 

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.