The security concerns, geopolitical uncertainties and pressure of global economic competition that have become evident in the European Union (EU) in recent years have rekindled fundamental debates about the Union’s institutional functioning and integration dynamics. At the heart of these debates, there is an integration model known as differentiation integration and usually defined as two speed or multiple speed Europe. This approach is since in an expanding and heterogeneous Union, it is not structurally possible for all member states to advance at the same speed and depth in every policy area. In this framework, it is envisaged that countries that are willing and capable to progress in certain areas will take the lead through “strengthen cooperation”, while others will participate in the process later or stay permanently out in certain areas. Especially in the recent period, the increase in hybrid threats facing Europe, the intensification of economic competition and the intensification of strategic dependence concerns have made this model a practical necessity.
In this framework, the radical transformation in European security architecture is the most critical driving force in the discussion. Because the perception of threat which radically shaped after Russia’s Ukraine invasion, brought the need for strategic autonomy even under the roof of NATO. Especially, uncertainties about the nature of the long-term engagement of the United States (USA) in European security have increased the search for more autonomous and sustainable capacity building in the field of defense in European capitals. Therefore, the tendency of existing common decision-making mechanisms to be inadequate in crisis situations has increased the demand for more flexible, fast and optional cooperation formats in areas such as defense capacity, military-industry cooperation and critical technologies. In this context, initiatives such as PESCO and the European Defense Fund aim to develop joint capacity and deepen defense industry integration, while military support to Ukraine through the European Peace Fund shows that the EU has evolved into a more direct and operational actor in the field of security. Similarly, narrower and more flexible formats, such as the European Intervention Initiative, developed under the leadership of France, reveal practical reflections of security cooperation models that do not have to cover all members. In addition, the European Political Community, which was established in 2022, has created a wider political and security coordination platform that includes European countries that are not members of the EU, indicating that a multi-layered and flexible integration architecture has been shaped across the continent.
These developments show that differentiated, two-speed and multi-speed integration trends in the field of security are embodied at the institutional and political level. However, this trend also brings with it the risk of excluding members who are not fully integrated into the EU’s common defense structures and creating a de facto “security core” within the Union. Because the core collaborations institutionalized in the field of defense can create a hierarchical structure in decision-making processes and make the position of countries with limited military capacity or neutrality policies controversial. Therefore, the differentiated, two-speed and multi-speed integration in the field of security has the potential to enable Europe to respond faster and more effectively to crises, while simultaneously deepening the center-peripheral division within the Union.
Similarly, the increasing intensification of global economic competition is further strengthening the two-speed or multi-speed differentiated integration debates in the European Union. China’s state-sponsored, economy-of-scale industrial capacity, with U.S. protectionist and incentive-oriented policies such as the Inflation Reduction Act, have made the EU’s technological dependencies and supply chain vulnerabilities clearly visible. In the face of these developments, developing common industrial policies at the European level and making coordinated investments in strategic sectors, especially energy, digital transformation and green economy, has become a necessity, not a choice. However, the lack of complete political agreement among the twenty-seven member states for such forward steps highlights flexible cooperation shaped around voluntary coalitions or core groups as a functional alternative, and in this context, areas such as the Defense industry, artificial intelligence and digital regulations, the green hydrogen economy, and critical raw material and supply chain security are also among the strategic policy topics in which such leading groups can make concrete progress.
Therefore, this model enables the EU to formulate policies that are both flexible and goal-oriented in the face of global competition, making it possible to take effective action even when full consensus among all members cannot be achieved. In this way, it not only allows for rapid decision-making in times of crisis but also facilitates the pursuit of Europe’s geopolitical and economic objectives in the long run, such as strategic autonomy and technological independence. In this context, differentiated integration in the form of two-speed or multi-speed Europe, along with the inherent logic of a core group, stands out as a significant potential mechanism capable of enhancing the EU’s economic resilience and strengthening its strategic room for maneuver under the pressures of global competition.
At the institutional level, the unanimity requirement within the European Union’s decision-making structure emerges as one of the key structural factors strengthening the idea of differentiated integration. As the number of member states has increased and divergences in national interests have deepened, the ability of a single country to block the Union’s decision-making processes through its veto has, in certain cases, created a structural constraint that can slow down or even halt the integration process altogether. It is precisely in this context that the “enhanced cooperation” mechanism provided for under the Lisbon Treaty gains prominence as an institutional tool, enabling at least nine member states to move forward collectively in a specific policy area. This mechanism not only facilitates faster decision-making in areas where full consensus cannot be achieved but also supports a flexible and multi-layered model of European governance, thereby offering an appropriate framework for the implementation of differentiated integration approaches such as two-speed or multi-speed Europe. In this respect, enhanced cooperation stands out as a pragmatic instrument that allows the EU to respond swiftly and effectively in times of crisis, while also encouraging progress through a core group logic and gradually paving the way for the broader participation of other member states over time.
On the other hand, the two-speed or multi-speed differentiated integration model offers both a theoretical and practical framework, allowing integration to progress at different speeds and depths in the face of the increasing heterogeneity of the European Union. From a neofunctionalism perspective, the deepening of a core group by leading certain policy areas can encourage participation by creating a spill-over on other member states over time. As a matter of fact, the Schengen Area and the Euro Area initially came to life with limited participation but then expanded with the involvement of more members in the integration process. The intergovernmental approach, on the other hand, evaluates this model as a balance mechanism between national sovereignty concerns and the need for collective action; It sees it as a low-cost and pragmatic institutional solution that prevents the integration of different national interests from blocking. Therefore, the two-speed or multi-speed integration serves as a third pathway or intermediate formula between the complete cessation of integration and the simultaneous and fully harmonious deepening of all members. It is possible for core groups to develop flexible collaborations, especially in priority and urgent areas such as security, defense industry, digital transformation and strategic industry policies. Such collaborations can enable rapid and effective policy production in the short term, while encouraging the participation of other members in the process over time, contributing to the progress of European integration in the long term in a sustainable, inclusive and strategic autonomy-based manner.
Nevertheless, it can be argued that the model of differentiated integration, commonly referred to as two-speed or multi-speed Europe, entails significant risks and dilemmas for the European integration project. The institutionalization of core group formations may deepen the center–periphery divide within the Union and reinforce feelings of exclusion, particularly among smaller member states or those with differing political positions. Therefore, the principle of solidarity, which constitutes a fundamental pillar of the EU, may be weakened, while the production of common policies risks being replaced by temporary and fluctuating coalitions. Moreover, the increasing ambiguity of integration prospects for candidate and enlargement countries may limit the Union’s normative appeal and reduce Europe’s external influence. For this reason, the sustainability of this model depends on structuring core groups according to an inclusive logic, extending the gains achieved to other member states, and effectively managing internal inequalities. Provided that these conditions are met, differentiated integration in the form of two-speed or multi-speed Europe can enhance short-term effectiveness while also fostering the long-term advancement of European integration based on legitimacy and solidarity.
When a general assessment is made, the discussion of two-speed or multi-speed differentiated integration is directly linked to the tension between expansion and deepening, which is the main structural dilemma of the European Union. Because while the ongoing enlargement process inevitably transforms the Union into a more heterogeneous and multi-phonic political structure, the heating of global competition and increasing security threats make faster, deeper and collective actions an urgent necessity. The current geopolitical environment forces the EU to become an effective global player, and this strategic goal requires flexible institutional mechanisms that can make agile decisions in critical areas, from defense policies to industrial strategies, from energy security to technology dominance. In this context, while differentiated integration offers a functional and pragmatic solution in the short and medium term, it also raises fundamental questions about the institutional character, goal and governance model of European integration in the long term. Therefore, the main strategic issue facing the EU is to establish a sustainable balance between geopolitical autonomy and the search for effectiveness and intra-united integrity, solidarity and democratic legitimacy. If this balance cannot be achieved, differentiation ceases to be an engine that advances integration and risks creating permanent hierarchies, a multi-layered structure and institutional divisions within the Union. Such a situation will bring with it not only the loss of efficiency, but also the erosion of the normative foundations and social acceptance of the European project.
