In January 2007, four senior US statesmen – George Shultz, William Perry, Henry Kissinger and Sam Nunn – wrote a seminal opinion piece in the Wall Street Journal, in which they called for a drastic reduction of the existing nuclear arsenals of the United States and Russia to reduce the chance of nuclear war and to prevent terrorist groups from gaining access to nuclear weapons (Shultz et al. 2007). A newly elected President Obama announced in April 2009 in Prague that great efforts would have to be made to make the world free of nuclear weapons. New START, a treaty between the United States and Russia, was subsequently signed, committing both countries to reduce their operational nuclear weapons to 1,550 each. In June 2013, in Berlin, President Obama renewed the call for further reducing US/Russian nuclear arsenals by a third, to around 1,000 weapons each (Cortright and Väyrynen 2010). However, the momentum for abolishing nuclear weapons seems to have stalled since then. Indeed, while nuclear-weapon states pledge nuclear disarmament, none of them has genuinely demonstrated a serious willingness to give up these arsenals. Nuclear weapons continue to feature prominently in their defence doctrines and military planning. In the United States, billions are being spent and are budgeted on extending the life-span of the existing arsenals and producing new nuclear warheads. Russia has recently announced it will introduce some 40 new ICBMs into its nuclear arsenal. Also, other nuclear-weapon states are engaged in increasingly expensive nuclear modernization programmes, with no signs of slowing down (Mecklin 2015; BBC 2015; Kristensen and Norris 2014). Meanwhile, the crisis in Ukraine and the Russia-West confrontation, heightened territorial disputes in East Asia and continuing tensions in South Asia further exacerbate the security dilemmas between rivalling states, many of them nuclear-armed. These developments cast a shadow over the prospects of nuclear disarmament and intensify interstate rivalry, while elevating the importance of extended deterrence and raising questions about it. All of these foreshadowed the 2015 NPT Review Conference, which ended with a failure to agree on a final document. What went wrong? And what must be done to renew and carry through the important task of achieving a world free of nuclear weapons, and to make sure nuclear disarmament will be irreversible, legal and permanent? Professors

Harald Müller and Andreas Persbo’s contributions to this volume seek to address these questions. For Professor Müller, a major obstacle to a nuclear-weaponsfree world (NWFW) is ‘the hegemony of existing mentalities’, in particular the fixation on deterrence to the extent that all other alternatives are not even considered in discussions of nuclear policy. For Müller, the very concept of nuclear deterrence (and hence the argument for its preservation, often by the organizations that benefit from it) constitutes a serious obstacle to nuclear zero. Müller rightly points to the illogic of the ‘virtual arsenals’ as part of deterrence. Essentially, any such arsenals are a guarantee that nuclear weapons will be retained, because any sensible governments would rather prefer the ready availability of nuclear arsenals, however shrunk they may be, to the ability and speed with which nuclear arsenals can be reconstituted, i.e. ‘the devil they don’t know’. Calling for the liberation of a cultural and psychological fixation on nuclear weapons, Müller believes the arms control and disarmament process itself can be transformative in reversing the military-industrial complex’s pursuit of armament and profits, which has been facilitated at times by transformative figures such as Reagan and Gorbachev – who had arrived at the same conclusion about nuclear weapons and nuclear war (‘A nuclear war cannot be won and must never be fought,’ said Reagan in his 1984 State of the Union address) and almost struck an agreement on abolition at the 1986 Reykjavik summit. But how would a world without nuclear weapons rid itself of the perennial curse of security dilemmas? Müller’s remedy is the formation of a concert of powers, very much like the nineteenth-century Concert of Europe, which secured a century of peace. Such a concert would fundamentally change the nature of relationships between great powers in an NWFW and should be built on the principles of equality, mutual respect for core interests, and an agreed governance structure. This concert of powers would not only provide the precondition for achieving a world free of nuclear weapons, but also serve as the enforcer of global and regional peace and stability through collective action. Müller is correct in pointing out that, while an NWFW could benefit from the existence of conventional deterrence, unilateral and asymmetrical distribution of long-range power projection (precision strike) capabilities could actually undermine strategic stability among the major powers. One way to address this is to limit the number of long-range precision strike missiles while at the same time developing and sharing ballistic missile defences. But, perhaps most importantly, Müller notes that for an NWFW to reach fruition and be maintained a fundamental step must be taken: a change in mentality, with the development and embracing of a new norm, a culture of minimizing and eliminating a role for nuclear weapons in national security, and a real taboo against the very existence of nuclear weapons, let alone their use in any conceivable way. This reference to the inhumane nature of nuclear weapons and the call for engaging religious groups to join the campaign to rid the world of nuclear weapons resonate with the recent international efforts to ‘identify and pursue effective measures to fill the legal gap for the prohibition and elimination of nuclear weapons’ (Reaching Critical Will 2015).