Originally published 2 June 2017.

Recent media reports ^[1] suggest senior US officials have told Julie Bishop that if North Korea’s nuclear weapon program can’t be reversed, South Korea and Japan will likely pursue their own indigenous nuclear arsenals. In fact, the proliferation chain might not be quite that straight-forward—in every proliferating country strategic logic has to coexist with a permissive political environment. But the strategic logic is certainly becoming more compelling. Compelling enough, at least, that Australia should be considering two important issues: what South Korea’s and Japan’s crossing of the nuclear threshold would say about the continuing credibility of the US doctrine of extended nuclear deterrence; and how Australia’s own nuclear identity might shift in a more densely-proliferated world. Both questions are so important that they merit some discussion during Monday’s AUSMIN dialogue, despite the already-crowded agenda ^[2].

Let’s start with the first—and simplest—question. If South Korea and Japan were to decide they needed their own nuclear arsenals, their decisions would suggest, strongly, that the age of the US nuclear umbrella was drawing to a close. The credibility of US nuclear assurances would face a challenge as fundamental as that posed by French proliferation back in the 1960s, but in an environment marked by greater anxiety over Washington’s constancy. US allies around the world would re-visit their own degree of faith in such commitments—and any such reassessment would, of course, be influenced by the fact that two of their number, both essentially status quo powers, had already abandoned the church.

True, Japan’s and South Korea’s particular strategic motivations wouldn’t necessarily be replicated among all US allies and partners. Nor would all enjoy the opportunity to cross the nuclear Rubicon in relatively short order—an option that exists for Tokyo and Seoul because of their extensive civil nuclear capabilities. But the honest assessment must be that defection by two principal US allies would be grievously felt, and might even precipitate the collapse of the broader doctrine of extended nuclear deterrence.

If that was to happen, we could easily find ourselves living through an age of sudden, intense nuclear proliferation. Current geopolitical uncertainties—already disruptive and disintegrative—might crystallise in an unpleasant fashion. The Taiwanese, the Poles, the Germans, the Saudis, the Turks and the Egyptians, for example, might follow the South Koreans and the Japanese. Holding Iran away from a bomb would become much more difficult. Within a decade or two we could be living in a world with around 20 nuclear-weapon powers, not just the current nine.

In relation to the second question—about Australia’s nuclear identity—it’s important to confront the central question right up front. If South Korea and Japan decide they’re unable to rely upon US extended nuclear deterrence, does it make sense for Australia to continue to do so? For it to add up, we’d need to have a convincing argument about why we were more strategically important to Washington than the two allies in the North Pacific—so making it more credible that the US would run nuclear risks on our behalf that it might not on theirs. That’s going to be a challenging argument to make, and it would only become more challenging in the wake of further defections from the current nuclear order.

Extended nuclear deterrence makes most sense in a low-proliferation world where the nuclear-weapon states are risk-averse great powers, because the risks the guarantor runs on behalf of its allies are few and unlikely. But it makes less sense in a densely-proliferated world, where guaranteeing to run risks on behalf of others is a much more fraught enterprise. Each new proliferator tears at the plausibility of extended nuclear deterrence, but risk-tolerant proliferators do particular damage. The upshot is that the concepts of extended deterrence and assurance make good sense in a world of five nuclear-weapon states, less sense in a world of ten, and almost no sense at all in a world of twenty.

Over recent years, Australian government ministers and official documents have had little to say about nuclear deterrence in general and extended nuclear deterrence in particular. Still, it’d be wrong to conclude from that limited evidence that Australia would be indifferent to the folding of the US nuclear umbrella. On the contrary, any such development would excite the most serious reconsideration of alternative strategic options since Australia signed the NPT in 1970. In a densely-proliferated world, the costs of remaining a conventionally-armed middle power would probably rise steeply. In his chess-themed novel, The Queen’s Gambit ^[3], Walter Tevis brutally describes the Caro-Kann Defence as ‘all pawns and no hope’. Future Australian governments—of whatever persuasion—would be reluctant to allow their defence policies to be described in similar fashion.