In 1983, 13 countries began negotiations on the treaty that would eventually form the South Pacific Nuclear-Weapons-Free Zone. To some, the resulting Treaty of Rarotonga was seen a symbolic gesture, since all but one negotiating state, Vanuatu, had already committed to their non-nuclear status through the Nuclear Non-Proliferation Treaty (NPT). Others criticized the zone as ‘porous,’ arguing that flexible provisions designed to achieve consensus would prevent progress on nonproliferation and arms control objectives.1 Yet even during negotiations, the energy of the anti-nuclear movement enabled a dramatic departure from the status quo. In 1984, New Zealand declared that it would no longer allow nuclear-armed or nuclear-powered ships to enter its ports. After three decades of the trilateral nuclear alliance between the Australia, New Zealand, and the United States (ANZUS), New Zealand decided to fold up its nuclear umbrella for good. While the move was unprecedented, New Zealand’s leaders did not anticipate serious opposition, expecting the United States to be flexible to the domestic concerns of an ally.2 That assessment proved to be wrong. After months of negotiations failed to shift New Zealand’s stance, the Reagan administration cancelled ANZUS defense exercises and informed New Zealand that the United States no longer considered itself bound to protect New Zealand’s defense, ending the collective security agreement central to the ANZUS pact. The unexpected forcefulness of the U.S. response illustrates how U.S. officials understood the stakes involved. The United States refused to identify to New Zealand which ships were nuclear-armed and powered – a relatively simple way to assuage the concerns of the latter and preserve the alliance – citing a long-standing policy of ambiguity. While this policy was officially justified in security terms, the specifications of U.S. vessels made it relatively simple to deduce which ships carried nuclear weapons.3 More importantly, ambiguity provided cover to allies for whom U.S. nuclear weapons had become a thorny political issue. Allied governments preferred not being able to definitively confirm that their ports hosted U.S. nuclear weapons and hoped to circumvent domestic pressure to cease the practice. U.S. officials feared that the example of New Zealand could revitalize debate in other allied nations, which had experienced substantial opposition to hosting nuclear-armed and powered ships.4 New Zealand did not reverse course, in spite of strong pressure from an asymmetrically powerful ally. In arguably the hardest test, public resistance to a nuclear-based defense proved to be resilient against the attractions of extended deterrence. The issue of hosting nuclear-armed ships soon faded from prominence when the United States removed tactical nuclear weapons from its ships. President George H. W. Bush announced in 1991 that the nuclear tomahawk (TLAM-N) would be removed from naval vessels. President Bill Clinton determined in 1994 that surface ships would no longer be capable of launching nuclear weapons. President Barack Obama decided in 2010 to officially retire the TLAM-N, then land-locked in warehouses for almost two decades. Defense relations with New Zealand, however, only began to thaw in 2012. The case of New Zealand is important to consider today. The 2018 Nuclear Posture Review (NPR) proposes the development of a new sea-launched cruise missile, resurrecting both the retired TLAM-N and the political flashpoints that ruptured an alliance. More broadly, though, the case of New Zealand illustrates how a bellicose nuclear posture can undermine, rather than augment, U.S. alliances. U.S. extended deterrence is an undeniable security asset in the eyes of most U.S. allies, but so are the institutions that sustain arms control and nonproliferation. These institutions are faltering. Maintenance of the status quo, much less progress, on bilateral arms control between the U.S. and Russia remains a bleak prospect. Though nuclear powers are committed to pursue disarmament in good faith under Article VI of the NPT, which the 2018 NPR calls “the cornerstone of the nuclear non-proliferation regime,” non-nuclear powers have not managed to extract substantive concessions from nuclear powers since the negotiation of the Comprehensive Test Ban Treaty (CTBT) began in 1994. The NPT was indefinitely, and optimistically, extended the following year, yet in the 2018 NPR the United States has abandoned even the premise of the CTBT’s ratification. Meanwhile, the 2015 NPT Review Conference failed to achieve consensus, and it seems unlikely that the 2020 Review Conference will fare better. Like New Zealand and the South Pacific Nuclear-Weapons-Free Zone, some are seeking alternative paths to constrain the behavior of nuclear powers. The Treaty for the Prohibition of Nuclear Weapons (TPNW), negotiated by over 120 states in 2017, demonstrates that the international community is losing faith in the grand bargain enshrined in the NPT. The TPNW is symptomatic of existing weaknesses in the NPT, but it also places new pressure on U.S. allies that cooperate, directly or indirectly, with U.S. nuclear posture, threatening their relationships with international partners and upsetting domestic political dynamics. Like the Treaty of Rarotonga, the nuclear ban has been criticized as either a redundant measure or one that is not sufficiently rigorous to affect change. But, just as in 1984, it would be a mistake to dismiss the influence of nonproliferation and disarmament norms on the strategic calculus of allied states. In this context, changes to U.S. nuclear posture have the potential to destabilize the difficult balancing act of U.S. allies. U.S. partners will find it increasingly difficult to argue for a step-by-step disarmament process if the United States itself is apathetic to the process,5 reversing a three-decade commitment to reduce its reliance on nuclear weapons. The 2018 NPR contrasts a safe world, in which politicians are free to ruminate on the dreams of arms control and nonproliferation, and a dangerous world, in which idle aspirations must be shed in deference to hard security challenges. However, this assumed incompatibility between security requirements and arms control ignores difficult trade-offs that come with an expansion of U.S. nuclear forces. The ramifications of even ‘minor’ adjustments may be deeply felt by alliances and institutions that play a vital role in supporting U.S. security interests. At minimum, advocates for those adjustments should acknowledge the risk that New Zealand might not always be an exceptional case. FootnotesMogami, Toshiki. “The South Pacific Nuclear Free Zone: A Fettered Leap Forward,” Journal of Peace Research, Vol 25, Issue 4, pp. 411-430. December 1988. Clements, Kevin. Back from the Brink: The Creation of a Nuclear-Free New Zealand, Allen & Unwin, Wellington, pp. 104. June 1988.Sutter, Robert. “Crisis in U.S.-New Zealand Relations: Issues for Congress,” CRS Report No. 85-92 F. February 26. 1985.Kristensen, Hans M. “Declassified: U.S. Nuclear Weapons at Sea,” Federation of American Scientists. https://fas.org/blogs/security/2016/02/nuclear-weapons-at-sea/.Kulesa, Lukasz. “The 2018 US Nuclear Posture Review: a headache for Europe,” European Leadership Network. https://www.europeanleadershipnetwork.org/commentary/the-2018-us-nuclear-posture-review-a-headache-for-europe/.