‘Thus far, the key objective of military strategy has been to win wars. From now on, the key objective of military strategy must be to avert wars. There can be no other objective.’

So wrote Bernard Brodie, one of the key strategists of the early nuclear age, whose writings still inspire and shape debates about how nuclear weapons affect international politics. The formulation epitomises what other scholars would later call ‘the nuclear revolution’: the transformational effect nuclear weapons would have on international statecraft, making war less, not more, likely.

The theory posited that the catastrophic effect of nuclear wars would be apparent to all, meaning many states would seek nuclear weapons and the ability to use them to respond to aggression. Having achieved such a secure second-strike capability, however, such states would fall back and relax their inherent impulse for competition and expansion, leaving the world a more peaceful place.

This theory always remained just that: a mere belief that could not explain the way states with nuclear weapons behaved after they acquired them. In recent years, substantive new critiques of the nuclear revolution theory have emerged, substantiating claims that the theory does not align with reality. And yet, the revolutionary and transformational effect of nuclear weapons continues to affect international relations and debates. Although the mere presence of nuclear weapons did not necessarily produce a more peaceful world, many still surmise that the lack of direct great power confrontation may be ascribed to their existence.

Almost 70 years after their ascendancy, the risk of the use of nuclear weapons in conflict seems larger than ever. Although the Russian invasion of Ukraine reignited such scenarios in the popular imagination, resurgent great power rivalry over the last decade has steadily elevated the risk of nuclear war. In Asia, the Taiwan scenario looms large, with questions on both sides regarding their adversary’s nuclear intentions. In Europe, any direct confrontation between Russia and NATO or the United States could rapidly turn nuclear, as per Russian promises of nuclear first-use in any large-scale conflict. Scenarios for great power nuclear escalation look perilous in northern Europe, home region of Russia’s secure second-strike force. Are nuclear weapons not the ultimate bringers of peace, reducing the potential for great power confrontation? Does the nature of contemporary great power rivalry undermine the apparent deterrent, and thus peaceful, effects of nuclear weapons?

Nuclear weapons are, for all practical purposes, the ultimate insurance and a guarantee of security for the states that possess them. But those states conceive of their deterrent effect in distinct ways; integrate them with their conventional military forces in distinct ways; and have distinct ideas about precisely how they can most effectively influence or shape adversary behaviour. A range of different factors impact such deliberations: geography, other military capabilities, perceptions, traditions and strategic culture.

Geography matters because the types of military threats states face are contingent on their geographic and strategic environment. A state with a large landmass encompassed by potential adversaries perceives graver and more pressing security threats than an isolated island. An ability to conceal military capabilities in the depths of the Siberian plains means that even states at a greater distance from Russia have to assess grave security issues.

Capabilities matter because states think differently about how nuclear and conventional weapons interact and affect their adversary. Russian nuclear policy is the furthest developed theoretically, if not practically, in the contemporary era, while states such as Pakistan, and alliances such as NATO, have historically also capitalised on the link between conventional inferiority and nuclear compensation. China currently deliberates on this question in altogether distinct ways.

Perceptions matter because states formulate policy based on their understanding and interpretation of their potential adversary: their capabilities may seem frightful even if they believe their benign intentions are entirely clear. As nuclear deterrence remains an essentially psychological enterprise, playing on cognitive dynamics such as fear, perceptions of nuclear capabilities and intentions matter more for international outcomes than perceptions of conventional military capabilities.

Traditions and culture matter because existing nuclear weapon states, including Russia, the US and China, all have decades of experience and large bureaucracies devoted to formulating nuclear policy and sustaining the nuclear enterprise. These complexes have their own idiosyncrasies and look different, and the strategic problems they face look different – which in turn produces differentiated solutions to these issues.

This variation in nuclear states’ behaviour has been explored in contemporary writing, but this area of scholarship has not yet produced a body of work that explores what such variation may look like and how its dynamic produces separate international behaviours. One empirical case in point is the unfolding war in Ukraine, a nuclear-laden conflict that holds differentiated lessons for a range of the world’s nuclear-armed and nuclear-aspiring states. A common lesson drawn from Ukraine, however, is that nuclear weapons may be conceived as even more useful than they are in reality, according to who is attaching strategic value to them.

Russian nuclear rhetoric and signalling during the Ukraine war is unprecedented. Many fear that Russia is learning a key lesson: aggression under the threat of potential nuclear escalation brings fewer risks. The presence of the world’s largest nuclear weapons arsenal is likely the key reason US forces are not currently deployed on a large scale in Kyiv. Russia’s conventional performance has demonstrated that, in such an alternative reality, it would have been unlikely to take and hold any part of Ukrainian territory over a prolonged period.

Nevertheless, another lesson Russia may be drawing from this conflict is that nuclear threats and bluster only bring them so far. Repeated threats have not affected the Ukrainian will to fight and defend their country. Russian leadership may still be concerned about the military utility of nuclear weapons use and whether it would outnumber the political costs associated with crossing the nuclear threshold. Yet it seems prone to continue to maximise the theoretical utility of the largest nuclear arsenal in the world; not least in a period when its conventional military force is cut down to size, and when its immediate environment has turned ever more hostile.

Through its unprecedented nuclear bluster, Russia is also gaining novel experience in how its threats, combined with other coercive measures, affect adversaries, producing political and military effects. Russia is likely watching Western responses with great interest and taking notes. It openly conveys that in a war with NATO, and facing a threatening, conventionally superior force, it would consider nuclear use. Some question the credibility of nuclear threats to pursue aggressive goals in Ukraine. Fewer might question the credibility of threatening nuclear use to preserve state existence.

The United States, other Western nuclear-armed states and NATO as a collective are drawing other nuclear lessons from the conflict in Ukraine. To them, this war demonstrates once and for all the nuclear addiction of an adversary like Russia. It has demonstrated how any potential conflict would have a substantial nuclear component, on or before the first day of fighting. Nuclear weapons would constantly and consistently affect the course of such a war. The likelihood of nuclear use on European territory would increase dramatically. Although security circles have been primed to this reality for some time, the war has brought home this reality to Western policymakers in a distinct way.

Because of this challenge, NATO is renewing its nuclear competency, and trying to do so fast. Security policy communities across the Atlantic are debating the most effective deterrence or influence on a nuclear-armed adversary. Most agree a modernised and reliable nuclear capability is a necessary component. Nuclear weapons will be a more important part of NATO’s deterrent mix in the years to come. The NATO summit communiqué from Vilnius in July 2023 signalled as much through its rejuvenated nuclear language.

The war in Ukraine has demonstrated to most of Europe the importance of, as well as the reliance on, a US security guarantee, including its nuclear umbrella. This point is one that American allies in the Asian-Pacific theatre have appreciated in a much more explicit way for some time. Japanese security and defence policy is transforming, with or without a nuclear component. South Korea has actively sought a more comprehensive conventional counterforce capability to influence North Korean nuclear calculations. Deterrence dynamics in the Asian-Pacific theatre are being revisited, both by novel developments, such as the AUKUS collaboration, and by observations and interpretations of the nuclear dynamic at play in the European theatre.

China may be drawing yet other nuclear lessons from the Ukraine war. Some fear that the country would draw similar conclusions to Russia regarding the potential for aggression under the shadow of nuclear escalation. The US, among others, has been doing its best to dissuade China that such aggression would go unpunished in the context of Taiwan. Chinese nuclear strategy suggests it is still upholding lessons about the strategic utility of nuclear weapons for coercion. Some argue China is betting more on other key military technologies in order to escalate and exert pressure on its adversaries. At the same time, China is also seeking to solidify its nuclear deterrent – in part perhaps in response to a perceived potential lower threshold on the part of the US to bring nuclear weapons into a direct confrontation.

These differentiated lessons all point in the same direction – that of an elevated role for nuclear weapons in a range of state military and political strategies. Furthermore, they point to an evolution where nuclear weapons may play a greater role in regional dynamics across the world. This includes Europe and its northernmost corner.

A new security policy landscape is being shaped in Europe, with the ongoing war in Ukraine, NATO measures to enhance deterrence and defence, and an ongoing expansion of NATO in the north. This new pattern is likely to have implications for the future.

It will take a lot to convince European states, at some point in the future, that Russia is not a force or threat to be reckoned with. It will take a lot to convince a future Russia, even with different leaders, that the type of force NATO is now generating across Europe and in its border regions harbours no aggressive intentions towards Russia. We are watching a new iron curtain descend on Europe. The question is whether we are paying sufficient attention as to how it can be changed to something more constructive.

The greater relevance of nuclear weapons to both Russia and to NATO is likely to have direct implications for its northern corner. This is already the case: Scandinavians live very close to a key area of Russian strategic retaliatory capability on the Kola Peninsula. In Norway and NATO, people have long been used to the strategic dilemma and confrontation this poses in the Barents and Norwegian Seas, as well as to Atlantic sea-lines of communication. In case of war between Russia and NATO, their interests will clash directly in Europe’s northernmost corner, regardless of where the war starts.

An expanded NATO will change the strategic landscape in a part of a traditionally low-tension part of Europe. It will likely be a question of time before this will affect Russian calculations and force dispositions. If no conventional forces are available, nuclear forces are the backup that the Russians resort to, also for signalling purposes. The peacetime situation is likely to become more tense in the years to come. A crisis or war will have a substantive nuclear component right on Europe’s doorstep, with potential implications for how countries fare in wartime.

Finally, differences in how Russia and NATO respectively think about the integration of nuclear and conventional forces will impact force dispositions in our region. As we have seen in the Asian-Pacific theatre, countries increasingly covet conventional counterforce or counterstrike capabilities. NATO may covet Russia’s nuclear capabilities, but NATO’s conventional capabilities are what Russia fears the most. New technologies impact how adversaries perceive their own critical vulnerabilities.

The new iron curtain in a transformed Europe is likely to produce novel dynamics and different hotspots of tension. Northern Europe will not be inoculated from this development; striking the right deterrence balance to minimise the risk of nuclear confrontation will place greater demands on European security and policy leaders – greater than most have experienced in their lifetime. Heavily rests our common responsibility to ensure that future nuclear policies bring peace rather than war.