Flexible Integration Geometry. Alternative Differentiation of the EU’s Defence and Security Policy Integration After 2022.

After 2022 the EU has fundamentally transformed its approach towards security and defence policy. Russian full scale invasion on Ukraine exposed critical limitations in the Union’s institutional capacity for collective action while simultaneously creating unprecedented political momentum for deeper integration. This paper aims to examine the emergence of alternative differentiated integration forms such as ad hoc cooperation frameworks leading to breaking the deadlock on integration in the field of security. Through systemic analysis this paper sheds light on the EU’s security and defence adaptation process and situates it within the new intergovernmentalism paradigm. The reaserch investigates the reconfiguration of the EU defence system through emergent patterns of differentiated integration, analysing how member states navigate between collective actions and persistent divergences in strategic preferences, military capabilities and threat perception. By utilising systemic analysis as the methodological framework, the study maps the complex interdependencies, feedback mechanisms, and adaptation processes that characterise the EU’s evolving defence governance structure. Focusing on the external-outside-inside-alternative differentiated integration enables systematic examination of how changes in the external security environment interact with the institutional dynamics to produce novel forms of flexible cooperation. The empirical investigation explores five interconnected dimensions of alternative integration. First, coalitions of the willing have emerged as a primary vehicles for rapid response capability. Second, the European Political Community represents institutional innovation creating inclusive, pan-european dialogue space transcending EU membership boundaries. Third, extra-institutional bilateral and multilateral defence agreements have proliferated, including strategic partnerships, capability-sharing arrangements, and integrated force structures negotiated outside EU auspices. Fourth, regional initiatives have been revitalised, with the Weimar Triangle, Visegrád Group, and Three Seas Initiative developing distinct security profiles reflecting geographic proximity to threats, shared historical experiences, and complementary strategic interests. Fifth, flexible geometry manifests through ad-hoc cooperation formats and variable participation frameworks where state involvement varies by capability domain, operational theatre, and resource commitment level. This creates overlapping integration circles rather than linear core-periphery differentiation. The research demonstrates that alternative differentiated integration represents systemic adaptation enabling European defence cooperation to advance despite institutional constraints and preference heterogeneity. The paper concludes by assessing whether multi-format, flexible cooperation architecture represents sustainable system responding to the principles of strategic autonomy, NATO complementarity, and the future of the trajectory of European security integration in an increasingly contested geopolitical environment.