“We will have to be ready for a day when America will withdraw its troops from Europe.
Then, European countries, and Germany in particular, will find themselves next to this Russian colossus with all its expansive impulses.
We thus have to do everything in our power not to be caught unarmed if a challenge ever comes.”
Konrad Adenauer
“You were given the choice between war and dishonour.
You chose dishonour – and you will have war.”
Winston Churchill
Foreword
"Ukraine, Nuclear Deterrence, and the New Proliferation Dynamic" emerges at a moment when the very foundations of the post-1945 international order are being tested. Russia’s aggression against Ukraine since 2014 and 2022, and the unprecedented use of nuclear threats in support of offensive war, has forced policymakers, scholars, and societies to confront questions that many believed were settled decades ago. The research presented in this publication seeks to examine these challenges with clarity and urgency, recognising that Ukraine’s security is not an isolated concern but is intrinsically bound to the stability of Europe, NATO, and the global non-proliferation regime. Reaktion Group is deeply grateful to Konrad-Adenauer-Stiftung Kyiv for supporting this work and for recognising the critical importance of grappling with these issues now, before the strategic environment deteriorates further.
This publication does not advocate for nuclear proliferation. Quite the opposite, its purpose is to illuminate the risks that arise when the norms and guarantees underpinning the global non-proliferation system are violated. Ukraine’s experience illustrates how the erosion of trust in treaties, alliances, and international commitments can fuel debates about nuclear latency or armament not only in Kyiv, but globally. By analysing the drivers behind these trends in Ukraine, South Korea, and beyond, this study aims to strengthen the international norms that have helped keep the world safer for decades. A secure, sovereign, and resilient Ukraine is essential not only for European stability, but also for ensuring that the Non-Proliferation Treaty and the broader rules-based order remain credible. Supporting Ukraine’s defence and deterrence therefore remains one of the most effective tools available to prevent the dangerous spread of nuclear weapons.
Finally, I would like to express my sincere gratitude to my team at Reaktion Group. Their dedication, expertise, and tireless commitment – often under challenging conditions, especially in wartime Ukraine – made this project possible. Their work reflects the seriousness of the moment and the shared belief that rigorous analysis can help shape a safer and more stable future for Europe, Ukraine, and the wider international community.
Joshua R. Kroeker
CEO & Founder, Reaktion Group Consulting Ltd.
Executive Summary
Russia’s full-scale invasion of Ukraine has become the most consequential challenge to the contemporary security order and the global non-proliferation regime. At the heart of this crisis lies the failure of the Budapest Memorandum, a political agreement through which Ukraine relinquished the world’s third-largest nuclear arsenal in exchange for security assurances that ultimately proved unenforceable. Russia’s serial violations of these assurances, first in 2014, then in 2022, have undermined confidence not only in political guarantees but in the very foundations of nuclear restraint. The war demonstrates how a nuclear-armed state can use both conventional force and nuclear intimidation against a non-nuclear neighbour, while the international community remains constrained by escalatory fears and geopolitical divisions.
Ukraine’s experience reveals the limits of legal commitments and highlights the centrality of credible deterrence – whether conventional, nuclear, or alliance-based. Russia’s systematic nuclear threats have shaped Western decision-making, slowed the provision of advanced weapons, and eroded long-standing norms around nuclear signalling. Meanwhile, Ukraine has shown that robust conventional capabilities, such as long-range strike systems and cost-imposing drone and missile operations, can undermine a nuclear-armed adversary’s freedom of action. Yet these capabilities cannot substitute for structural security guarantees, especially as both Ukrainian manpower and Western support face growing strain. In this context, some in Ukraine argue that regaining a nuclear deterrent is the only truly reliable option for the country despite significant technical and political hurdles.
The implications of this extend far beyond Europe. States such as South Korea, observing the collapse of Ukraine’s assurances, are also openly debating nuclear options, questioning the credibility of U.S. extended deterrence, and drawing direct parallels between their own security environment and Ukraine’s. In Europe, the war has exposed profound deficiencies in defence capacity, strategic coordination, and political will, leaving the continent ill-prepared to deter further Russian aggression or to compensate for shifting U.S. priorities.
This study argues that preventing broader nuclear proliferation and ensuring Ukrainian sovereignty depends on a decisive strategic commitment from Europe and the wider West. Credible security for Ukraine will require sustained transfers of advanced conventional weapons, long-term defence-industrial investment, and political guarantees embedded within NATO or equivalent structures. The alternative is an increasingly unstable world in which states conclude that nuclear weapons, and not treaties, norms, or assurances, are the only reliable hedge against aggression.
The prospect of resisting Russian aggression at times is met with fears that the Russian state might disintegrate into chaos in the event of military defeat in Ukraine, with fragmentation of central power and the loss of unified control over the country’s nuclear weapons. It is, however, crucial to consider the limits of Western agency: if the Russian state is so far on the edge that such scenarios are in the cards, the structural factors that shape collapse options will bring them about sooner or later, regardless of the West’s policy choices with regard to Ukraine. Western capitals should prepare for these scenarios by building intelligence capacities, developing contingency plans, hardening domestic detection and defence systems, and monitoring key indicators in Russia, such as elite splits, failures to implement explicit Kremlin policy, breakdowns in federal budgetary streams, and active empire-building by local elites.
The choices made now, in Ukraine, will shape the future of nuclear deterrence and international order for decades to come.
