In times of crisis, Europe tends to improvise. In the wake of the US retreat from Ukraine and European security, European leaders are coming together to support Ukraine and take a greater responsibility for their own future security. As it stands now, neither the European Union (EU) nor the North Atlantic Treaty Organization (NATO) can provide Europe a sufficient framework for security cooperation. The United States (US) is resolutely unwilling to engage, which effectively rules out NATO. Meanwhile, several non-EU members are raising their hand to join a potential military coalition in Ukraine while several countries within the EU do not want to participate, effectively also ruling out the EU as a framework.

From the sovereign debt crisis to Russia’s invasion of Crimea, Brexit, and COVID-19, Europe has regularly grappled with the challenge of speaking and acting with one voice. Reverting to informal gatherings and ad hoc coalitions has repeatedly allowed European leaders that share a sense of urgency to overcome EU institutional and bureaucratic gridlock. In today’s European security context, discussions on ad hoc coalitions are again mushrooming.

The most pressing discussions are around the idea of deploying a military force composed of troops from a European-led coalition of the willing. This idea has been floated for several months now and is a subject of ongoing talks hosted by French President Emmanuel Macron and United Kingdom (UK)  Prime Minister Keir Starmer on how to ensure Ukraine’s security and take responsibility for European defense. While the contours of such a mission are unclear, including whether it should take the form of a deterrent force that can be deployed in the absence of a ceasefire agreement or a proper peacekeeping mission, talks are getting serious, and operational planning is underway, according to Starmer. The “willing” include EU members such as France, Sweden, Denmark, and Belgium, as well as non-EU states like the UK, Australia, Canada, New Zealand, Norway, and Turkey. The group of “unwilling” is an odd mix of countries with adversarial approaches to Russia that prefer to keep their troops at home for their own defense, like Poland, and more Russia-friendly countries like Hungary and Slovakia.

Ad hoc coalitions are also the dominant mode for coordinating military aid to Ukraine. The value of the eight “capability coalitions” coordinated by the Ukraine Defense Contact Group can hardly be overestimated: they fill critical capability needs of the Ukrainian Defence Forces while guaranteeing a minimum level of coordination and facilitating rapid response to Ukrainian capacity needs. Granted, two of these coalitions are co-led by the US (Air Force Capability Coalition and Artillery Coalition), but the majority are European-led coalitions (Integrated Air and Missile Defense Coalition, Armored Vehicles and Maneuverability Coalition, Maritime Capability Coalition, IT Coalition, Demining Capability Coalition, Drone Coalition).

Beyond Ukraine, more coalitions of the willing are also being formed to promote European defense cooperation more broadly. These tend to have a strong regional flavor. The Weimar triangle (Germany, France, and Poland) and the Benelux group are just a few examples. The French-led European Intervention Initiative and the UK-led Joint Expeditionary Force are also illustrations of this trend.

Today, one of the most influential of these coalitions is the Nordic-Baltic 8, a grouping that brings together the Nordic countries (Denmark, Finland, Iceland, Norway, and Sweden) and the Baltic states (Estonia, Latvia, and Lithuania). Since the start of the war in Ukraine, their influence has grown considerably, with the accession of Finland and Sweden accelerating military and political cooperation among the members. Coalitions like these not only facilitate collective decision making in times of crisis but also contribute to doctrinal alignment, interoperability of national armed forces, and the development of shared strategic cultures.

Pitfalls of a Coalition Approach

As both NATO and the EU—in their foreign, security, and defense policies—operate with consensus or unanimity, coalitions of the willing will continue to play a decisive role in the medium term for the security of both Ukraine and Europe. However, Europe should be careful not to overly depend on a coalition approach. Four years of research on coalitions of the willing—or ad hoc coalitions, as we label them—in international security through our ad hoc crisis response and international organizations (ADHOCISM) project tells us that they have obvious benefits, allowing for rapid action by states that are bound by a shared sense of threat, urgency, and purpose. Yet there are also several risks and pitfalls to relying on coalitions.

First, ad hoc solutions lack democratic legitimacy and mostly have no, or only weak, accountability frameworks. In the long run, this may backfire, leading to declining public support or a chaotic coming and going of contributing states driven by domestic politics.

Second, without being institutionalized, coalitions do not lead to institutional learning. For better or worse, Ukraine is the frontline of the future of modern warfare. Allied states are already busy with rethinking their future capability needs and doctrinal frameworks. A coalition of the willing must be enabled to learn and convert experiences on the ground into updated EU and NATO doctrinal frameworks.

Third, and most importantly, the desire to move quickly can come at the expense of embedding the coalition in a longer term political-diplomatic strategy. Without this, it is unlikely that the coalition will contribute to solving the root causes of security crises. It is therefore essential that operational coalitions of the willing are backed by a comprehensive political dialogue among the contributing states.

In sum, while ad hoc coalitions are all the rage in today’s debates about Ukraine’s security and European defense, they are mostly stop-gap measures. Coalitions are good at filling holes in the ship, but they don’t usually put a sail on it.

Anchoring Coalitions in a Long-term Strategy

To be truly effective, coalitions need to be anchored in an institutional approach—in this case either through NATO, the EU or a combination of both. The capability coalitions are a case in point. In the summer of 2024, these were augmented by the establishment of the NATO Security Assistance and Training for Ukraine (NSATU), a 700-strong organization in support of the capability coalitions operational from January 1, 2025. Nevertheless, with the current uncertainty around the US and NATO, future support to Ukraine will continue to be provided through various ad hoc formats. Similarly, European states will have to develop new formats to strengthen European security and provide troops to Ukraine.

We therefore recommend that future investment in coalitions for European and Ukrainian security are synergized with EU and NATO frameworks to ensure complementarity and to anchor them in a longer-term political-diplomatic strategy.

• While allied support is provided, it is still too little and too late. In the short term, financial and military aid to Ukraine can continue to take place through the NSATU and the capability coalitions, but these coalitions should be accompanied by a real sense of urgency, so that the required military resources are delivered faster, with more predictability and where they are most needed.
• A military deployment by a coalition of the willing will ultimately require a credible backstop. A European coalition of the willing that is not backed up by a credible deterrent and not allowed to make use of vital NATO assets, such as air surveillance and intelligence, is unthinkable. In other words, such a military force should ideally take the form of a European NATO force, most likely without US boots on the ground, but ideally with US endorsement.
• For European defense more generally, any coalition effort needs to be firmly embedded in an EU strategy to consolidate the European defense industry, promote joint procurement, and facilitate public and private investment. There is also a need for rapid action on joint ventures in areas such as ammunition production, including with Ukraine’s defense industry. As an example, Ukraine is using less than 50% of its current drone production capacity. It is in Ukraine that the largest potential currently lies to speed up production.
• Importantly, ad hoc coalition efforts that are not grounded in long-term strategies are likely to end up as strategic failures. Ukraine’s allies should therefore develop a clear and uniform understanding of the desired end state of a military mission in combination with a vision for how to sustain security guarantees, integrate Ukraine’s defense industry into a European defense industry, and rebuild the Ukrainian economy.

Coalitions of the willing are the talk of the town these days and will play a central role in the future security of Ukraine and Europe. Yet, European leaders should not forget that coalitions are only stop-gap measures and anchoring them in a longer-term political-diplomatic strategy is essential.

John Karlsrud is a Research Professor at the Norwegian Institute of International Affairs (NUPI). Yf Reykers is Assistant Professor in International Relations at the Faculty of Arts and Social Sciences at Maastricht University.