Promises, Power, and Protection: The West’s Debate Over Security Guarantees for Ukraine
Speaker: Iulian Romanyshyn, DAAD/AGI Research Fellow
Moderator: Jeff Rathke, President and Director of the Foreign & Security Policy Program, AGI
President Trump’s deal-making efforts to bring Ukraine and Russia to the negotiation table have so far not delivered. Even though a ceasefire—let alone a peace agreement—between Kyiv and Moscow remains elusive, accelerated diplomacy has raised the question of Ukraine’s long-term security, sharpening the link between the need to end the war and to construct a credible security guarantee. Ukrainian leaders have stressed that any meaningful security guarantees against Russian aggression need to be backed up by Western military force and political resolve. This, however, sits uneasily with the Trump administration’s approach, which has ruled out Ukraine’s membership in NATO, signaled its willingness to restore economic relations with Russia, and declared that Ukraine’s postwar security is the responsibility of European allies.
There is a great deal of political debate about a potential ceasefire or negotiated settlement. However, these debates have not elaborated on how to sustain the negotiated deal or what to do if Russia violates it by resuming aggression with renewed strength and bolstered resources. What capabilities does Ukraine need to effectively deny or punish another Russian invasion? What are the role and prospects of Western military presence in Ukraine? How does the credible commitment to Ukraine’s defense recalibrate transatlantic relations?
Dr. Iulian Romanyshyn is a senior fellow and lecturer at the Center for Advanced Security, Strategic and Integration Studies (CASSIS) at the University of Bonn. He is also the head of the scientific program at the Institute for International Cooperation, Technological Diplomacy and Communication (ICI) and an advisor at CMI – Martti Ahtisaari Peace Foundation. He previously held research and teaching positions at New York University, Maastricht University, Free University of Brussels, and European University Institute, as well as research fellowships at the NATO Defense College, the Academy of International Affairs NRW, and the Charlemagne Prize Academy. Iulian holds a PhD in political science from the IMT School for Advanced Studies Lucca, master’s and bachelor’s degrees from Maastricht University, College of Europe (Bruges), and the National University of Kyiv-Mohyla Academy.
Iulian’s research focuses on transatlantic security relations, EU security and defense policy, Black Sea security, and EU-Ukraine relations. He has published widely in many peer-reviewed journals, including the Journal of Common Market Studies, International Journal, Journal of European Integration, European Foreign Affairs Review, International Politics, and European Security, and contributed to a number of leading think tanks, including the Atlantic Council, Carnegie Europe, and the German Institute of Development and Sustainability. Iulian’s research has been acknowledged with the Global Strategy PhD Prize awarded by the Egmont Institute for International Relations and the European Security and Defence College.
Event Summary
This webinar examines how the transatlantic community can credibly deter a renewed Russian aggression against Ukraine. The central argument is the following: in the absence of NATO’s protective umbrella in the immediate term, a meaningful security guarantee for Ukraine must be built on country’s own military capabilities. This core element can be complemented but not replaced by other measures, such as a European military presence on Ukrainian territory, a snapback mechanism of sanctions on Russia, and enhanced societal resilience across Europe.
The presentation grounded the discussion in classic deterrence theory. Deterrence was defined as dissuading an adversary from taking unwanted action by threatening unacceptable consequences. Its success depends on both capability (the means to impose costs or deny success) and credibility (the perceived willingness to use those means). Deterrence by denial convinces an adversary it cannot achieve its objectives, and deterrence by punishment threatens severe costs after an attack.
The session assessed why deterrence failed in February 2022. In the lead-up to the full-scale invasion, most deterrent threats were framed as post-invasion punishment, with almost no effort to preempt or deny a rapid Russian victory on the ground. Public statements by senior U.S. officials suggesting that Kyiv might fall within days further reinforced an image of Western disengagement. As a result, there was little “fear of failure” through denial and limited “fear of pain” through punishment in Moscow’s calculus.
Debates over security guarantees have evolved under different U.S. administrations. Under President Biden, various models of NATO membership for Ukraine were discussed, but ultimately, the administration declined to endorse membership in the short term, citing escalation risks and lack of consensus among key European allies, including strong resistance in Germany. Instead, the United States promoted a network of bilateral security agreements between Ukraine and individual NATO/EU states. These agreements provide political commitments and pledges of assistance but fall short of binding mutual defense guarantees.
With the Trump administration, U.S. views shifted more fundamentally. The current administration operates on three core assumptions: the United States does not have vital security interests in Europe, the war in Ukraine is primarily a European problem, and a Russian victory in Ukraine does not constitute a major U.S. national security threat. NATO membership for Ukraine was explicitly taken off the table and attention turned to economic ideas such as a “mineral deal” in which Ukraine’s security would supposedly be underpinned by U.S. investment. Early on, Washington stressed that Europeans should assume responsibility for Ukraine’s long-term security. Only later did the president acknowledge the need for security guarantees, offering a vague promise to help Europeans deploy a reassurance force in Ukraine after a ceasefire, without specifying the nature or scope of U.S. support.
This contrasts with U.S. public opinion. There is broad support among American voters for continued weapons deliveries and sanctions. Across party lines, a clear majority believe Ukraine should receive security guarantees from the United States if it commits to negotiating an end to the war.
The core of the proposed guarantee, however, lies in Ukraine’s own armed forces. Ukraine now fields roughly 900,000 people in uniform and spends about 34 percent of its GDP on defense, the highest military burden in the world. Over more than a decade of war, the Ukrainian military has developed substantial combat experience and is regarded as the central tool of any deterrence regime. Nonetheless, significant gaps remain. The most critical shortfall is air defense, essential for denial-based deterrence against Russia’s sustained missile and drone attacks on Ukrainian cities and infrastructure. Another key gap is long-range strike capabilities: Ukraine needs large numbers of cruise and ballistic missiles with ranges exceeding 1,000 kilometers to threaten what the Russian regime values most, particularly energy infrastructure and arms production facilities.
Ukraine’s defense industry is a major emerging pillar of deterrence. According to Ukrainian officials, around 60 percent of weapons now used at the front are domestically produced, and Ukraine could potentially manufacture up to 20 million drones in the coming year—ten times the 2024 output—provided adequate financing is secured. Current industrial output is approximately $35 billion, but the Ukrainian state can finance only half, leaving a significant funding gap. This raises the question of how partners can create sustainable, institutionalized mechanisms to finance Ukraine’s defense production and move to a more predictable framework that delivers what some analysts call a “qualitative deterrence balance.”
The supplementary element in the proposed model is a European reassurance force on Ukrainian territory. The idea of sending Western troops was first floated publicly by French President Emmanuel Macron in February 2024 and initially met strong resistance, especially from Washington and Berlin. After the shift in U.S. policy, France and the United Kingdom announced in March 2025 the formation of a European “coalition of the willing” to support Ukraine’s sovereignty and underpin a possible future ceasefire. By September 2025, twenty-six countries had declared their intention to contribute in some form to this reassurance mission.
The force was described in two potential formats. A maximalist version would consist of 60,000 to 80,000 combat-ready troops forming a rapid reaction force capable of supporting Ukrainian operations and helping to break Russian defensive lines if Moscow violated a ceasefire. A minimalist version would focus on training and capacity building, especially in combined-arms operations, as well as guarding critical infrastructure and sensitive borders. In both cases, European troops would form a second line of defense; Ukrainian forces would remain responsible for frontline combat.
Forward-based European troops in Ukraine would significantly raise credibility by physically tying European security to Ukraine’s fate and increasing interdependence between Ukraine and NATO. They also enhance denial, because any renewed attack would immediately involve not only Ukrainian units but allied forces. Forward deployment was presented as the clearest indicator of willingness to fight, or “skin in the game,” and thus a central missing element in the failed deterrence of February 2022.
However, serious challenges remain: European governments will continue to depend on U.S. strategic enablers such as intelligence and logistics; it is unclear whether Washington would intervene if European troops in Ukraine were attacked; financial pressures and personnel shortages in France, the United Kingdom, and others may limit the duration and scale of deployments; and important European military actors such as Germany, Italy, and Poland have been hesitant or openly skeptical about sending troops.
The primary security guarantee for Ukraine must come from within through maximized indigenous capabilities, a strong domestic defense industry, and unrestricted operational use of Western weapons. European troops in Ukraine are an essential interim supplement until NATO membership becomes feasible, both to deepen the security link between Ukraine and Europe and to correct the current imbalance in which Russia has dominated the escalation ladder. Ukraine is already beginning to shift from security consumer to security provider, citing recent instances in which NATO members requested Ukrainian assistance against Russian drones. The overarching conclusion was that, unless the West demonstrates a clear willingness to fight, Russia will not be effectively deterred.
This event is supported by the DAAD with funds from the Federal Foreign Office.
