New START Expiry: Implications for Europe

Today, 5 February 2026, the last US-Russian arms control agreement – the New Strategic Arms Reduction Treaty (New START) – expired. Concluded in 2010, the Treaty placed quantitative limits on warheads deployed on US and Russian strategic delivery systems (ICBMs, SLBMs and heavy bombers), as well as on the numbers of deployed and non-deployed strategic launchers. New START also provided for extensive reporting, verification and risk reduction measures to support the Treaty’s effective implementation. New START was the last remaining piece of arms control infrastructure between Russia and the US; Washington withdrew from the Anti-Ballistic Missile (ABM) Treaty in 2002 and the Intermediate Nuclear Forces (INF) Treaty in 2019 (citing Russian violations), with Moscow withdrawing from the Conventional Armed Forces in Europe (CFE) Treaty in 2023.

Russia suspended its ratification of New Start in 2023; today, the Treaty officially expired. At the last minute, reports emerged that the US and Russia were nearing an agreement to extend the terms of the treaty for a limited amount of time. At the time of drafting, the details of the reported agreement (for instance, whether it would include compliance with quantitative limits only or if it would also see the resumption of data exchanges and inspections), or the likelihood that it would concluded at all, were not clear. As one US official is reported to have noted, any continued compliance with New START limits would have to rely on a ‘handshake’ deal, seeing as the Treaty does not allow for further formal extensions. Regardless, this comes as a welcome development, in a strategic environment in which both Moscow and Washington both have incentive to expand their strategic capabilities.

However, should the New START and the limits it placed on US and Russian strategic forces indeed collapse, the direct impacts of New START for Europe are likely to be limited – at least in the short term. The treaty did not address the systems of most direct concern to Europe – namely, theatre nuclear forces – and neither Russia nor the US is in a position to begin a major nuclear buildup. What is of greater importance than the end of the treaty itself are the strategic conditions that accompany its expiry, which persist and which will determine key features of Europe’s security environment.

Doomed from the Start

The completion of New START – and the arms control architecture established between Moscow and Washington over the course of the Cold War and in the years that followed its conclusion – was an impressive achievement in more ways than one. The agreement ran counter to both US extended deterrence and Russian incentives to hedge against a perceived first strike risk. The frameworks thus defied strategic gravity for longer than might have been expected.

A key consideration here is the demands on US forces created by US extended deterrence commitments with the US being perennially challenged to prove it would trade ‘Washington for Bonn’. During the Cold War and into the post-Cold War period, US advantages in intelligence, surveillance and reconnaissance (ISR) missile accuracy and the ability to track SSBNs helped mitigate these fears by sustaining the prospect of damage limitation. In principle, the United States could credibly threaten Russian strategic forces while retaining sufficient survivable capability for follow-on strikes. Escalation on behalf of European allies, in other words, did not automatically entail the certainty of national annihilation. It was never a given such damage limitation would succeed, considering the sheer scale of the Soviet – and later Russian – arsenal. Yet, by reducing the inevitability of catastrophic retaliation through the maintenance of a large strategic nuclear arsenal, the United States made extended deterrence more credible than it would otherwise have been.

Yet this logic always carried an inherent tension: the same capabilities that enable damage limitation can also be perceived as elements of a first-strike posture, a point well understood in both Moscow and Washington. As figures involved in Cold War negotiations understood, what the US defined as parity and a balance necessary to make its commitments credible, the Soviets would see as US superiority. This inherent asymmetry makes arms control implacably difficult. When arms control agreements did occur in the past, they often did so against the backdrop of a wider lessening of tensions (for example the era of détente) which reduced the salience of the finer points of the nuclear balance in policymakers’ eyes. However, the shaky foundations on which agreements rest have meant their de facto or de jure abrogation has always been more likely than not in periods when tensions inevitably resurfaced.

For contemporary Russia, this tension has been compounded by two developments which drive Russian thinking on its strategic balance with the US. The first is the emergence of (for the time being) US conventional prompt strike capabilities capable of engaging elements of Russia’s nuclear forces that previously could only be targeted with nuclear weapons. This substantially expands the set of systems Russia must consider when assessing threats to its deterrent. The weight of the US advantages in virtually every other facet of power was always likely to impact the nuclear balance in ways that problematised the START framework.

The second is the prospect that improved US missile defences could provide a degree of homeland protection sufficient either to blunt a calibrated Russian response to a largely conventional first strike, or to intercept residual forces after multiple waves of attack. Russia’s development of systems such as the RS-28 Sarmat – capable of carrying up to fifteen MIRVs (multiple independently-targeted re-entry vehicles), compared to the ten carried by the R-36 it replaced – has reflected an intent to preserve the ability to rapidly exceed New START limits on deployed warheads if required. Russian officials, including then Deputy Defence Minister Yuri Borisov, explicitly framed Sarmat’s heavy payload as a response to US missile defence. In parallel, Russia has pursued novel systems such as the nuclear-powered Poseidon torpedo and Burevestnik cruise missile, which lay entirely outside the treaty framework.

The structural difficulty of sustaining New START’s limits has since been compounded by a further factor: the rise of China as a conventional – and increasingly nuclear – peer of the United States. Beijing has expanded its nuclear arsenal at breakneck pace over the last few years; the US intelligence community expects China to have an arsenal of 1500 warheads by 2035. This necessarily impacts on US assessments of how big – and what kind – of a nuclear force is enough to deter not one but two adversaries, while also providing for the maintenance of a credible extended deterrence posture. Steps the US takes to rectify perceived imbalances vis Russia and China, taken collectively, will look to each party like the US widening a lead it enjoys, in bilateral terms, over the concerned state. This concern was articulated recently by Admiral Igor Kostyukov, Deputy Director of the GRU, who argued the deployment of US missiles in East Asia constituted a threat to Russia’s Strategic Missile Forces.

A dynamic that was already unstable in a dyadic setting thus becomes untenable in a triangular relationship: the United States is compelled to reason about deterrence in collective terms, while each adversary continues to judge US capabilities solely against its own bilateral balance.

The Question for Europe

The expiry of New START limits could – in theory – allow for the expansion of US strategic forces to address the two-peer deterrence challenge. However, any progress on this front will take time to materialise, if it does at all. The total (deployed and undeployed) numbers of strategic launchers in the Russian and US arsenals are currently within New START limits. Furthermore, the US and Russia are both already undertaking costly modernisation programmes to upgrade their existing strategic capabilities. Both programmes have been plagued by issues. On the American side the Sentinel ICBM has faced an 81 percent cost overrun while Russia’s RS-28 Sarmat ICBM has seen high profile test failures. As such, any significant expansion of strategic systems in the short term is unlikely. A more feasible option may be the uploading of additional warheads onto existing strategic systems. Furthermore, if a more permanent and formal extension of quantitative limits on strategic forces is not reached eventually, this period of limbo – depending on how long it lasts – may allow the two sides to position themselves to expand their arsenals at shorter notice if and when the restrictions finally collapse.

More to the point, because New START governed the strategic balance between Russia and the United States, it did little to constrain the Russian capabilities most immediately threatening to Europe – namely, non-strategic nuclear weapons. Russia maintains a significant quantitative and qualitative (in terms of diversity of systems) advantage. The UK and France do not possess non-strategic nuclear capabilities and have therefore had to historically rely on the credibility of US extended deterrence to deter limited Russian nuclear use in Europe. The implications of New START collapse for the credibility of US damage limitation capabilities therefore threaten to exacerbate anxieties in Europe over the credibility of US extended deterrence. However, public debate in parts of Europe and Canada over the need to develop national nuclear deterrents has made clear the extent to which that credibility has already degraded among allies in the face of apparent US disengagement from – and outright undermining of – European security.

Furthermore, it raises the possibility US efforts to manage this challenge are interpreted by Russia as a drive towards nuclear primacy. In such an environment, capabilities that might appear marginal in isolation can assume outsized significance, because Russia cannot rule out their employment in concert with US forces. Seen through this lens, senior Russian leaders’ public concern over Japan’s acquisition of 400 Tomahawk land-attack missiles – despite the limited number of missiles and their clear orientation toward China – becomes more intelligible.

The lesson for Europe is even limited investments in conventional strike capabilities by US allies can exacerbate Russian perceptions of vulnerability if these missiles are viewed as part of an aggregate imbalance, while further entangling the United States in European deterrence for the same reasons.

Conclusions

The demise of New START is emblematic of Henry Kissinger’s observation about how a certain technically oriented style of diplomacy often assumes the correct procedures can shape strategic outcomes. In reality, all institutions and procedures – including arms control agreements – rest on political and material foundations that lie well beyond their formal remit. New START was grounded in a set of conditions that were inherently fragile: a brief period of relatively cooperative US-Russian relations; a temporarily stable nuclear balance between two states otherwise unequal across most dimensions of power; and an increasingly artificial assumption of a purely dyadic nuclear order in a world where conventional capabilities can directly affect the nuclear balance. The collapse of the treaty should therefore come as no surprise. Should the treaty limits be extended, Russia and the US will still have a long road ahead of them to make sure that the restrictions can be sustained in the face of countervailing strategic winds.

Any future arms control initiatives will bring to the table a slew of new challenges to manage. Considering China’s quickly expanding arsenal, it is difficult to conceive of a sustainable arms control arrangement that does not account for the impact of China’s forces on the strategic environment. At the same time, Moscow has long been calling for France and the UK to be included in arms control efforts. Yet, both states maintain a minimal credible deterrent posture; as such, quantitative reductions in UK and French nuclear arsenals will remain a non-starter in the current strategic environment and until Russia – and by extension, the US – are ready to reduce their own arsenals.

The prospects for future arms control thus remain dim. Europe will need to consider not the question of how to restore a lost stability, but rather how to secure a position of relative security in a context that will be, by its very structure, inherently unstable.

© RUSI, 2026.

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