Non-Proliferation in an “Age of Nuclear Weapons”: Challenges and Prospects

An “age of nuclear weapons” and proliferation temptations

In his speech on nuclear deterrence at l’Ile Longue, French President Emmanuel Macron announced that “the coming half-century will be an age of nuclear weapons.”^[1]

Nuclear Weapon States (NWS) are increasingly relying on nuclear weapons to address the current challenges of the strategic environment. In recent years, the have been reaffirming the role of nuclear deterrence in their security strategies and investing heavily in the modernisation of their nuclear forces. But this trend is also visible among Non-Nuclear Weapon States (NNWS). In South Korea, Türkiye, Saudi Arabia, Poland, Germany, Ukraine, to name a few, political leaders have more or less clearly stated that possessing nuclear weapons could serve their countries’ security.

Against this backdrop, the international normative framework, and in particular the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) appears to be a weak barrier against proliferation temptations. This instrument has regularly been declared to be in crisis since the beginning of the century, even if it continues to demonstrate its resilience since only North Korea has withdrawn from it to become a nuclear-weapon state to this day. Nevertheless, strategic competition between powers, regional conflicts and dysfunctional multilateralism are creating incentives to launch national nuclear programmes, particularly in East Asia, the Middle East and Europe.

In this context, the strength of the norm remains an important factor in persuading states to remain NNWS. But there are also other factors that deter states from proliferating, such as belonging to an alliance with nuclear guarantees, the fear of international isolation, and the apprehension of military retaliation or prohibitive economic costs – both direct and indirect. These motivations need to be reassessed in light of the current crisis of multilateralism, doubts about the credibility of US security guarantees and the emergence of new security frameworks, especially in Europe.

The revival of nuclear deterrence

Major powers’ reaffirmation of their nuclear status

In February 2007 Vladimir Putin expressed Russia’s dissatisfaction with the post-Cold War international order, denouncing what he perceived as unfair treatment of his country and the West’s hegemonic ambitions. The following year, the war in Georgia showed Russia’s determination to use force to maintain some form of control over former Soviet republics. With the first crisis in Ukraine in 2014–2015 (annexation of Crimea and conflict in the Donbass), it became clear that Russia’s interventionism could call into question the foundations of European security. Russia demonstrated its intention to use a policy of “aggressive sanctuarization” with a strong nuclear component to alter the borders of a sovereign European state to its own advantage.

In Asia, while there are conceptual debates as to whether China is a revisionist or revolutionary power, it is clearly opposed to the post-Cold War international order in the Indo-Pacific. The main areas of tension are Taiwan, but also the South China Sea and the land border with India. More broadly, China explicitly seeks to reduce the United States’ influence in Asia, and to establish itself as the world’s leading superpower. Moreover, while Chinese developments in the nuclear field had been modest since the 1960s, rapid advances have been made in recent years, suggesting that Beijing seeks to establish itself as a leading nuclear power in the short to medium term.

While during the so-called second nuclear age (from the end of the Cold War until 2014, although the classification of nuclear ages is controversial) certain actors were considered deviants from the international order and were referred to as “proliferating” states, the consolidation of their nuclear forces now brings them into the equation of deterrence. Thus, despite the lack of diplomatic recognition of North Korea’s nuclear status, Western military staffs no longer simply regard Pyongyang as a proliferation problem but seek to build deterrence strategies against it. Indeed, the threat posed by North Korea’s nuclear strategy has major repercussions for the entire Indo-Pacific defence architecture. This is also true of the Indo-Pakistani dyad, whose nuclear rivalry extends beyond the Indian subcontinent because India is also involved in a strategic competition with China and some of its capacity choices reflect larger regional dynamics.

Increase of arsenals

The current phenomenon of “nuclear rearmament” goes far beyond traditional modernisation efforts. It is marked by the introduction of new capabilities that are likely to lead to greater dependence on nuclear forces, and by a sharp increase in several arsenals.

The most obvious case is China. Since the 1990s, China has progressively increased its arsenal while diversifying it (development of a naval component). In recent years, growth has been significantly faster. In 2021, the Pentagon told Congress that China’s arsenal was likely to double by 2025. In December 2025, the Pentagon declared that China would in all likelihood have an arsenal of over 1,000 nuclear warheads by the end of the decade.^[2] These developments call into question the Chinese government’s willingness to stick to the official posture of minimal deterrence and a strategy of retaliation.

On the Russian side, extensive modernisation programmes were launched in the 2000s to replace systems inherited from the Soviet era. Most of these modernisation programmes did not lead to changes in strategy or strategic balances, as they coincided with the withdrawal of older weapons. However, Russia’s non-compliance with the Intermediate Nuclear Forces (INF) treaty has enabled it to develop a potentially dual-use system (capable of carrying nuclear or conventional warheads) over previously prohibited ranges (between 500 and 5,500 km). Secondly, in 2018, Vladimir Putin declared his intention to equip the country with new capabilities that are often referred to as “exotic” insofar as they do not replace older systems and represent new types of missiles. This is the case with the Kinzhal air-launched ballistic missile, described by Russia as hypersonic, which, although currently used as a conventional weapon (for strikes in Ukraine), is deemed to have a nuclear capability. Another weapon developed for speed and precision is the Tsirkon hypersonic cruise missile, which presumably exists in a nuclear or conventional version. Two other systems have been announced and are currently under development. The first is an underwater drone known as the “Poseidon”. The second, a nuclear-powered cruise missile dubbed “Burevestnik” 9M730, will probably be the last to enter operational service. Finally, the Russian decision to station nuclear weapons on Belarusian territory is also a source of concern.

So far, the United States has not decided to increase its nuclear arsenal, but the expiration of the New Start Treaty in February 2026 removes the legal constraint on doing so, which is seen as increasingly necessary among parts of the strategic community. Thus, the Strategic Posture Commission, a bipartisan group of experts, recommended in 2023 keeping open the possibility of uploading additional nuclear weapons on existing platforms or even launching new programmes.^[3] It should be noted that major powers are not the only ones opting to expand their arsenals: the United Kingdom announced an increase of its stockpile in 2021^[4] and France did so in March 2026.^[5]

Increased fragility of the non-proliferation regime

Unresolved proliferation crises

While the NPT has been mostly effective in stopping the spread of nuclear weapons, a few cases show that multilateral nuclear regulations may not always prevent a determined state from pursuing a nuclear programme. Thus, North Korea withdrew from the NPT in 2003 under contested circumstances and has since developed an ambitious programme despite sanctions and international condemnation. Many states still declare that they support diplomatic endeavours to obtain the “denuclearisation” of North Korea, but this aim appears increasingly unrealistic as Pyongyang displays its attachment to nuclear deterrence to ensure the security of the regime.

In Iran, the nuclear programme initiated in the 1970s has led to decades of diplomatic engagement, active counter-proliferation efforts (including sanctions, sabotage and assassinations) and two military operations to this day. Yet all these endeavours may only have reinforced Tehran’s conviction that a nuclear capability is necessary to secure the regime. While many capacities have been either traded away or destroyed, the remnants of nuclear material and the uncertainty that surrounds the programme continue to be a destabilising factor in the region.

Tensions of the regime

As tensions rise and nuclear powers rely increasingly on their nuclear capacities, the international regimes built to curb proliferation and regulate nuclear competition are under strain. Thus, arms control agreements are collapsing, and contrary to a trend which marked the end of the Cold War, arsenals are again increasing. Within the NPT, this is perceived extremely negatively by most NNWS that feel that the “Grand Bargain” of the nuclear order is no longer respected. Indeed, article VI of the NPT calls on all states to “pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament.” For more than a decade now, no arms control agreement has been negotiated, and existing ones have either expired or collapsed. Measures such as the treaty prohibiting nuclear tests (CTBT) or the project to prohibit the production of fissile material for nuclear weapons have failed to enter into force or even to be adopted. Geopolitical tensions between NWS make it impossible to bring any tangible progress regarding disarmament to the table. Frustrated by this standstill, a group of NNWS negotiated and adopted the Treaty on the Prohibition of Nuclear Weapons (TPNW) in 2017. The disagreements surrounding this effort highlight the rift within the international community over the value and risks that nuclear weapons pose to global security.

This impasse in disarmament is also weakening the NPT’s other pillars. First, regarding proliferation, not only do some countries fail to comply with their obligations, but some NWS actually assist them by violating the regulations established by the UN Security Council and export control regimes. Finally, the targeting of civilian nuclear installations in military operations damages the credibility of commitments to the peaceful use of nuclear energy and to nuclear security.

Proliferation as a fatality?

Nuclear deterrence: ultimate provider of security?

At the time of the USSR’s dissolution, Ukraine was one of the Soviet republics where nuclear weapons were stationed. Like Belarus and Kazakhstan, it agreed to transfer them to Russia. In return, the Budapest Memorandum, signed in 1994 by Russia, the United States, and the United Kingdom guaranteed Ukraine’s territorial integrity; France, the other Western nuclear power, did so in a separate declaration. However, Russia’s annexation of Crimea in 2014 constituted a clear violation of this multilateral commitment. The fact that Ukraine and the international community were unable to protect the country’s territorial integrity highlights that a non-nuclear state remains vulnerable to aggression by a nuclear power and fundamentally dependent on the latter’s goodwill. The full-scale invasion of 2022 only reinforced this perception. Other countries that also renounced nuclear weapons, whether voluntarily or under duress and in different circumstances, have also suffered aggression and subsequently seen their regimes overthrown (Iraq in 2003 and Libya in 2011, and, to some extent, Iran in 2025 and 2026). States such as North Korea draw the de factoconclusion that a state which has agreed to dispose of its nuclear capabilities is highly vulnerable. Whilst this interpretation may be debated, it is gaining ground and, with it, the principles underpinning the international non-proliferation regime are being called into question.

Proliferation temptations in various regions

In this context, proliferation rhetoric is on the rise. In Asia, South Korea has historically been tempted to rely increasingly on nuclear weapons for its security. This has not only led to calls to reintroduce U.S. nuclear weapons on the peninsula, but also to a discussion about whether Seoul should develop its own nuclear weapons. This debate has intensified over recent years, displaying serious concerns in South Korea about the behaviour of its northern neighbour and the reliability of American support.^[6] More surprisingly, Japanese leaders have also begun to reconsider their position on nuclear weapons. Thus, there is currently a debate over whether the three non-nuclear principles adopted in 1967 – Japan’s commitment not to (1) possess, (2) produce, or (3) allow nuclear weapons into its territory or territorial waters – should be reconsidered.^[7] Although it was immediately disclaimed, a government official’s remark in 2025 that Japan might benefit from possessing its own nuclear force marks a further step.^[8]

In Europe as well, unexpected calls for nuclear rearmament have been voiced in recent years, driven by similar factors: a growing sense of threat and declining confidence in the US nuclear umbrella.^[9] During Donald Trump’s first term, there was a public debate in Germany, mostly in the press, about whether the country should develop its own nuclear programme. Trump’s re-election has revived this debate. In Poland, elected officials have shown even greater openness to such proposals. In a speech to the Diet in 2025, Prime Minister Tusk stated that Poland should consider developing non-conventional weapons, while President Karol Nawrocki ambiguously declared that Poland should “join the nuclear project”.^[10] Even in Sweden and other Scandinavians countries where the public has historically suffered from what could be called a “nuclear allergy”, columnists and former officials have made proposals for developing nuclear weapons.^[11]

In the Middle East, the Iranian nuclear crisis has fuelled uncertainty as to whether other regional powers are willing and able to acquire nuclear capabilities as well. In particular, Mohammed bin Salman’s statements in 2018 and 2021 suggest that Saudi Arabia would “follow suit” if Tehran managed to acquire the bomb.^[12] Türkiye could be another candidate for proliferation, given President Erdoğan’s ambiguous remarks about the unacceptability of the non-proliferation regime.^[13]

Options to restrain proliferation in a nuclear age

The power of norms

Does the NPT still retain binding force?

To this day, the NPT remains one of the most widely ratified treaties, and its states parties regularly reaffirm their support for its underlying principles at review conferences. While many NNWS highlight the treaty’s shortcomings (e.g., unequal status of states and lack of progress on disarmament), few contest the need to ensure that the vast majority of the international community remains free of nuclear weapons. This support is reflected in additional commitments undertaken by these states, such as the establishment of nuclear-weapon-free zones or the ratification of the TPNW.

This broad and enduring renunciation of nuclear weapons as a strategic option can, to some extent, be explained by constructivist theory.^[14] This school of thought emphasises the role of norms and states’ interest in promoting norms that are consistent with their identities and values. Whatever may have motivated states to sign the NPT, being a NNWS has, in many cases, become an inseparable part of their identity. In this case, the question no longer is to what extent refraining from nuclear weapons serves exclusively their “objective” national interests, since abiding by their own norms and promoting them on the international stage is an interest in its own right. An assumed NNWS identity alters an actor’s perception of security and thus its political and strategic calculus. Whether out of conformity, sincere conviction or identification with a group, the leaders of certain countries therefore wish to reflect the non-nuclear consensus that exists within their society and elevate their national preference to a collective one. Subsequently, the principle of continuity, as well as an emerging rhetoric of conviction, often commits actors to cling to their commitment not to embark on a nuclear programme.

The rational logic of non-proliferation

However, the non-proliferation norm is, more than anything, a collective, pragmatic conviction that all nations share a fundamental interest in preventing the spread of nuclear weapons. This norm was forged during an era of geopolitical instability. When the landmark Irish Resolution, which is regarded as a forerunner of the NPT, was introduced in 1958, tensions were abundant: the Berlin Crisis was intensifying, Fidel Castro’s ascent in Cuba shifted regional dynamics, and both the United States and the Soviet Union conducted dozens of atmospheric nuclear tests. During this period, active proliferation programmes were numerous, and nuclear accidents were a persistent reality. The underlying logic of the non-proliferation movement was born out of necessity: the international community recognised that the only path toward eventual disarmament was to freeze the expansion of nuclear arsenals and end hazardous testing. Even if they could obtain nuclear weapons themselves, states’ overall security would decrease if a vast number of states launched nuclear programmes. It was therefore rational to agree to constraints that would apply to all. This historical context mirrors the contemporary era, where non-proliferation remains a shared interest that transcends regional or national interests.

Allies’ politics and pressures

Costs to a nuclear programme

Normative pressure, as well as rational national interests, contribute to encouraging states to continue foregoing nuclear weapons. However, in the very short term, fear of costs also plays a major role. In the event of non-compliance with or withdrawal from the NPT, the matter is necessarily referred to the UN Security Council. Should the Council consider that such behaviour constitutes a “threat to peace”, it is within its mandate to take the necessary action, as set out in Chapter VII of the United Nations Charter. This is why North Korea and Iran have been heavily sanctioned by the UNSC due to their nuclear activities. Nevertheless, it is clear that the UNSC is inherently political and cannot take a decision if one of its permanent members opposes it.

Logically, proliferation has implications for international nuclear cooperation: it is no longer possible to envisage this type of activity if IAEA safeguards are no longer respected.

Over the years, many states have adopted a range of legislative measures designed to deter third countries from engaging in proliferation-related activities. In the United States, in particular, the Glenn Amendment (22 USC 2799aa-1(b)) has the effect of suspending commercial activities, military assistance and development aid with a state accused of seeking to develop or acquire a nuclear weapon. The Arms Export Control Act (22 USC 2753(f)) prohibits defence exports to a state that has violated its international non-proliferation commitments. The Foreign Assistance Act (22 USC 2429a-2) prohibits the provision of assistance to any NNWS which, in the President’s estimation, has terminated, abrogated or substantially violated its comprehensive safeguards agreement with the IAEA.

In Europe, the states party to the Euratom Treaty are bound by the principles governing the implementation of Article III of the NPT. Furthermore, in its bilateral agreements with third states, Euratom requires, as a condition for transfers, that the recipient state be able to implement its safeguards agreements, or even the IAEA Additional Protocol, in accordance with the NPT.

More broadly, the European Union has adopted legal instruments affirming its support for the NPT and its regime. Regulation (EC) No 428/2009 states that, in accordance with the arms control treaties and agreements signed by Member States, authorisations or prohibitions on transfers of sensitive materials or technologies may be based on whether or not the recipient has ratified the relevant international treaties.

Unless it operates in a virtually self-sufficient manner, a proliferating state would inevitably suffer major economic consequences across a wide range of sectors. However, these repercussions could be alleviated by the support of a major power that could block action at the Security Council, ignore export control regimes and decide to bypass or modify its own legislation. Thus, Chinese and now Russian support has been instrumental for North Korea and largely mitigated the impact of international sanctions. This unofficial support has given rise to the idea that “friendly proliferation” could be envisaged under the protection of the United States.

Does “friendly proliferation” exist?

The hope that the United States, in particular, may protect an ally tempted to acquire nuclear weapons, has fuelled a debate on the concept of “friendly proliferation”. Among conservatives in Washington, and sometimes within the circles of the Trump administration, some have considered that letting allies or partners develop their own nuclear capacities could be beneficial for Washington, as it would allow the United States to save resources for its own defence and to limit its strategic exposure.^[15] This idea has also been defended, for instance in the Korean context, as the most efficient way to deter nuclear adversaries.^[16] In reality, it is hard to imagine that the United States would tolerate proliferation, especially in Europe. To this day, the United States, but also Russia or China, have occasionally turned a blind eye to proliferation by their allies, but have in fact always been reluctant to the emergence of new nuclear weapon states, seen as potentially diluting their relative power and increasing strategic risks.

Moreover, if increasing fragmentation paralyses the international order and for instance makes UNSC mechanism irrelevant, it also means that each “patron” has less clout than previously. Thus, for an ally of the United States, it might be possible to hope that Washington would refrain from adopting strict sanctions following the revelation of proliferation-related activities, but this does not mean that it could escape all negative consequences. In Asia, Chinese economic reprisals could for instance be extremely harsh. In Europe, proliferation may lead to the implosion of the European Union as an alliance. Moreover, Russia has already used counter-proliferation as an excuse for its attack on Ukraine and could also pose a threat to an emerging nuclear country. In the Middle East, the risk of cascading nuclear programmes in the region, as well as preventive strikes against sites of concern, could be seen as a powerful deterrent.

Extended deterrence

The United States’ role in providing security guarantees

The costs of proliferation remain therefore objectively high around the globe. However, in the face of high threat, decision-makers may be tempted to minimise it. This is why since the Cold War, nuclear patrons, and in particular the United States, have been putting forward incentives for remaining NNWS. Thus, US extended deterrence has been regularly promoted as the most efficient non-proliferation tool. Within NATO, the deployment of US systems in Europe or the creation of consultative mechanisms have been considered as essential to reassure allies and divert them from the lure of a national nuclear programme. Recently, the efforts put forward by the Biden administration to reassure South Korea, for instance through the creation of a Nuclear Consultative Group and the announcement of new joint exercises in 2023 follow the same logic.

Both during his first and second term, Donald Trump has damaged this relationship, by downgrading the logic of solidarity towards allies for whom he and his team have shown little respect, encouraging purely transactional relations, favouring a closer and nationalistic approach, and making it clear that strategic interests may not be shared.

However, no member of the administration has actually called into question the validity of existing extended deterrence mechanisms. Under-Secretary for Defense Elbridge Colby has in fact positively confirmed that they are still functional.^[17] Both in Asia and Europe, allies continue to invest in increasing the credibility of US nuclear guarantees. So even if the link is damaged and the trust is diminished, the prospect of definitively severing the nuclear protection of such a strong ally as Washington because of a budding effort to develop a national capacity remains unappealing for a great majority of decision-makers.^[18]

“Forward deterrence”: a tool to curb proliferation in Europe?

Interestingly, in his 2026 speech, French President Macron supported the US logic of presenting extended deterrence as a non-proliferation tool. Thus, he declared that “the forward deterrence approach that we are proposing is not escalatory, and as it enhances the feeling of security in Europe, it provides significant benefits to prevent potential future risks of proliferation on our continent.”^[19]In the French mindset, thinking deterrence with a European dimension allows for a more credible tool to deter potential adversaries. Therefore, it puts European countries in a better position in the power balance. The idea is that different partners can contribute to European security by pooling their resources: for France and the United Kingdom, the nuclear forces are a major asset, but for other countries, conventional capacities play a huge role. This vision of a form of distribution makes proliferation detrimental to overall regional security. The French efforts have been generally welcomed by its partners, in particular the countries explicitly named by the President as cooperating with Paris on this issue: the United Kingdom, Germany, Poland, the Netherlands, Belgium, Greece, Sweden, and Denmark. However, doubts continue and will continue to be heard on the credibility of these proposals, and for some security experts or political leaders, this contribution will never be enough. The argument, which, ironically, was made in the 1960 by the French themselves, according to which one country should only depend on itself for its survival, will therefore find supporters as long as the level of threats remains so high.

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Geopolitical tensions, spread of conflicts, and an increased reliance on nuclear weapons are leading, in many countries, to a renewed debate about the desirability to develop national nuclear programmes. Those states have refrained so far from embarking on such developments, mostly out of respect for the non-proliferation norm, fear of the economic and political consequences, and to ensure the preservation of extended deterrence. The recent French assessment that its nuclear policy could contribute to increase incentives to respect the NPT within Europe feeds this logic. Ultimately, decision-makers rely on a cost-benefit analysis based on their threat perception and their understanding of the costs. This decision must take into account that individual choices have global repercussions, and by opting to develop nuclear weapons for themselves, they may open the way for a wave of proliferation that would decrease their security in the long term. It is this reasoning that led to the adoption of the NPT in 1968 and remains fundamentally grounded today.