The Euro-Atlantic region has in experienced a number of shocks and shifts over the last decades, ranging from the end of the Cold War and a newly emerged European security order to financial crises, and the most recent ruptures to Pax Europaea caused by Russia’s war against Ukraine. The existing European security order is shaped by a multiplicity of state and non-state actors, most prominently NATO and the EU, as well as by the recent trend of institutional fragmentation, diversity and complexity. While Euro-Atlantic security cooperation has traditionally been seen as a security community, a shift within its security order given the decline of US hegemony can be observed. Understood as regional cooperation driven by multiple powers within a region, this shift is reflected by the emergence of minilateral security cooperation (MSC) frameworks in addition to established regional security organisations, which are centred around different poles within the Euro-Atlantic region. This yields to questions about the implications of minilaterals for the European and Euro-Atlantic regional security order.

This article draws attention to member states' diverging interests of the Euro-Atlantic security order, namely Germany, Poland, and the US, and seeks to explore their approaches to initiating and leading minilateral security cooperation in the context of a changing regional security order. It argues that Germany initiates minilaterals as a way of bypassing calls for greater leadership in European security, Poland creates them to gain greater leverage due to lower levels of economic and military power, while the US, in contrast, seeks to foster its dominant role in transatlantic security through creating MSC in the context of its declining hegemony in Euro-Atlantic security.

In recent years, EU decision-makers have used differentiation as a mechanism to resolve decision-making deadlocks and integration crises. As a core state power governed by the unanimity rule, the Common Security and Defence Policy has been a notable example of this practice, employing differentiated cooperation to enhance the EU’s defence capacity (Hoeffler 2019, Blockmans and Crosson 2019, Klose et al. 2023, Rieker and Giske 2023). We argue that using differentiation as a flexible governance framework, which enables EU member states to overcome legal obstacles, has its own limits. Beyond internal selective participation, CSDP initiatives allow for third-country involvement, primarily to mobilise additional resources to address geopolitical challenges. However, the EU's external differentiation in defence faces a significant barrier: national security. By situating the analysis within the broader debate on differentiation in EU foreign, security, and defence policy, this study contributes to a deeper understanding of how flexible integration mechanisms function in areas marked by high sovereignty sensitivity. In doing so, it provides an empirically grounded perspective to the ongoing scholarly discussion on the limits and strategic implications of differentiation as a crisis management tool for fostering collective action within the CSDP framework.

After decades of underinvestment, military mobility has re-emerged as a critical component of European security and defence. While recent debates have largely focused on rearmament, the credibility of NATO deterrence on the Alliance’s eastern flank depends equally on the rapid cross-border movement of forces and equipment. Since 2014—and with heightened urgency following Russia’s full-scale invasion of Ukraine in 2022—both NATO and the European Union have prioritised military mobility as a domain of intensified cooperation. This article analyses military mobility through the lenses of minilateralism and policy transfer, understood as a process in which ideas, rules, and administrative arrangements developed in one political setting influence policy development in another, mediated by EU institutional structures. Empirically, it examines the Military Mobility Area (MMA) established in 2024 by the Netherlands, Germany, and Poland. The MMA is conceptualised as a bottom-up policy experiment that enables the uploading of national practices to the EU level and their subsequent downloading across member states. The findings show that the MMA has facilitated regulatory and procedural convergence, but that implementation remains uneven due to national caveats, infrastructural constraints, and fragmented EU–NATO governance. The article argues that military mobility exemplifies an emergent mode of EU security governance in which minilateral initiatives function as laboratories for EU-wide solutions, while also exposing the limits of bottom-up approaches in the absence of stronger supranational coordination and investment.

Centred on the Common Foreign and Security Policy (CFSP) and its institutional aspects, most EU scholars have scrutinized treaty-based flexibility mechanisms as solutions to overcome stalemate and contribute to a stronger EU foreign policy actorness. Against this backdrop, Russia’s war of aggression against Ukraine since 2022 has revigorated the debate on a “normalisation” of the CFSP, notably in favour of an extension of the application of Qualified Majority Voting. In this same context however, while witnessing unprecedented EU institutions centrality, the EU foreign policy response to the war has increasingly manifested outside of the formal CFSP framework, through informal, ad hoc arrangements. Drawing insights from the EU’s response to the Russia-Ukraine conflict before and after the full-scale invasion through the ‘Normandy’ and ‘Coalition of the Willing’ initiatives, this article proposes to move beyond the focus on the CFSP, and examine instead the normalisation of adhocism and its contribution to a stronger EU foreign policy actorness.