When the historical development of European integration is examined, it can be seen that the processes of enlargement and deepening have been the fundamental dynamics shaping the institutional, political and economic transformation of the Union. European integration initially emerged as a project aimed at establishing lasting peace across the continent through economic interdependence, and over time evolved into a more comprehensive political structure through the development of common institutions, the harmonization of national policies, and the strengthening of supranational decision-making mechanisms. However, the relationship between the expansion of the Union’s geographical scope and the enhancement of its institutional depth has been reshaped at every stage of the integration process under the influence of different political and economic priorities. Particularly with the accession of Central and Eastern European countries to the Union following the end of the Cold War, an important stage was reached in overcoming Europe’s historical division and ensuring democratic stability across the continent. However, the increase in the number of member states through the 2004 and 2007 enlargements also brought new institutional problems in areas such as the effectiveness of decision-making processes, economic convergence, and the feasibility of implementing common policies. This historical experience has demonstrated that enlargement is not limited merely to an increase in the number of members, but is also a multidimensional process requiring the restructuring of the Union’s institutional capacity, financial resources, and common political will.
The geopolitical transformations that have taken place in the international system in recent years have brought the historical tension between enlargement and deepening to a more complex dimension. In particular, Russia’s annexation of Crimea in 2014 and its large-scale military intervention against Ukraine in 2022 directly affected Europe’s security architecture and led to a reassessment of the European Union’s policies toward its eastern neighborhood. These developments have brought security and geopolitical stability objectives to the forefront alongside the conditions on which enlargement policy has traditionally been based, such as democratization, the rule of law, economic convergence, and the adoption of the acquis. In particular, the strengthening of the membership perspectives of Ukraine and Moldova, the renewed strategic importance of the long-standing accession processes in the Western Balkans, and the search for a stable political space along Europe’s eastern borders demonstrate that enlargement has evolved from a technical harmonization mechanism into a strategic policy area affecting the Union’s position in the international system. In this framework, while enlargement has the potential to expand Europe’s geopolitical sphere of influence and limit the regional influence of third actors, it also envisages ensuring the candidate countries’ compliance with democratic standards, the rule of law, and common European values. However, although geopolitical priorities have gained greater weight in the membership process and increased expectations for accelerating enlargement, the consistent application of membership criteria remains important for preserving the Union’s normative legitimacy and institutional integrity.
As a result of this transformation, gradual integration and phased membership models are gaining greater importance in the European Union’s enlargement policy. While meeting the Copenhagen criteria, aligning with the acquis, and completing the negotiation processes stand out as the fundamental conditions in the traditional accession process, the gradual integration approach envisages the phased participation of candidate countries in certain policy areas and economic mechanisms before full membership is achieved. In particular, the Growth Plan developed for the Western Balkans aims to facilitate candidate countries’ access to certain parts of the European Single Market, support economic reforms, and deepen regional economic integration. This approach enables the relations of candidate countries with the European Union to move beyond being dependent solely on progress in membership negotiations and allows economic and institutional integration to be developed at earlier stages. For example, phased access to strategic areas such as energy, transportation, digital infrastructure, industry, and trade is expected to strengthen the economic resilience of candidate countries and contribute to their more comprehensive alignment with European values and regulatory standards. However, although gradual integration imposes economic obligations on candidate countries, its provision of limited opportunities for participation in decision-making processes may create a structural asymmetry between representation and responsibility. If the membership perspective is not linked to a clear timetable and predictable conditions, gradual integration may cease to be a temporary transitional mechanism and turn into a permanent intermediate status. Such a development may strengthen the perception of second-class partnership among candidate countries while also weakening the transformative effect of the membership process and political support for reforms. Therefore, designing gradual integration not as an alternative to full membership, but as a complementary mechanism based on merit and preserving the ultimate goal of membership, is important for the sustainability of enlargement policy.
The institutional and financial dimensions of the enlargement process are directly connected to discussions concerning the European Union’s future political structure. An increase in the number of member states may make it more difficult to preserve the effectiveness of existing decision-making mechanisms, while it may also increase the reflection of economic and political differences among member states in the formulation of common policies. The application of the unanimity principle, particularly in strategic areas such as the Common Foreign and Security Policy and taxation, is one of the main areas where the tension between national sovereignty and supranational decision-making capacity becomes evident. While unanimity enables member states to protect their vital national interests, it may also lead to common decisions being delayed or blocked due to the objection of a single state. Therefore, extending qualified majority voting to more policy areas is among the reform proposals aimed at preserving the decision-making capacity of an expanding Union. However, considering that the right of veto serves as a safeguard, particularly for small and medium-sized member states, against the political and economic weight of larger countries, the transition from unanimity to qualified majority cannot be assessed solely on the basis of administrative efficiency. This change also represents a more comprehensive institutional transformation concerning the areas in which national sovereignty will be shared with common institutions, how the political equality of member states will be protected, and through which mechanisms the democratic legitimacy of common decisions will be ensured. Indeed, the European Commission’s approach to enlargement considers it necessary not only to prepare candidate countries for membership, but also for the Union to achieve the institutional capacity to accommodate a larger membership structure. In this context, restructuring decision-making mechanisms is one of the prerequisites for enlargement, while it is also important that reforms be implemented without creating new political divisions among member states.
In this framework, the institutional reform debates that have recently been rising in the EU will inevitably have important consequences in terms of the structure of the European Commission and the representation of member states within the executive body. The presence of one commissioner from each member state within the Commission serves an important function in terms of national representation and institutional legitimacy. However, an increase in the number of member states as a result of enlargement may create new difficulties in terms of determining the areas of responsibility of commissioners, ensuring policy coordination, and effectively conducting decision-making processes. Today, proposals such as limiting the number of commissioners, developing a rotating representation system, or reorganizing the distribution of responsibilities are being discussed within the EU to overcome these problems. However, limiting the expectation that every member state should be represented within the Commission may increase concerns, particularly among smaller countries, about being excluded from decision-making processes. Therefore, the balance to be established between institutional efficiency and political representation will inevitably be one of the fundamental governance problems the Union will face after enlargement. In other words, while differentiated integration models offer flexible mechanisms for addressing this problem, they also carry the risk of fragmenting the common legal and political structure. For example, some member states moving toward deeper integration in certain policy areas while others remain at a more limited level of participation may cause European integration to evolve into a multi-layered structure. On the one hand, this may facilitate the management of different national priorities within a common institutional framework, while on the other hand, it may lead to the emergence of different categories of rights and obligations among members. Therefore, the sustainability of differentiated integration depends on preserving the common treaty framework, clearly defining transition mechanisms between levels of participation, and maintaining the validity of fundamental legal principles for all member states.
Another important issue facing the European Union in its enlargement process is the sustainability of financial resources and the ability of existing budget mechanisms to adapt to the accession of new members. The Multiannual Financial Framework is the fundamental financial mechanism determining the Union’s spending priorities in policy areas such as agriculture, regional development, research, innovation, infrastructure, energy, and external relations. The accession of new members will require not only an increase in the size of the budget, but also a reassessment of the distribution of existing resources and spending priorities. In particular, Ukraine’s possible membership stands out as a development that could have significant effects on the Common Agricultural Policy and Cohesion Policy due to its extensive agricultural production capacity, population, and need for economic reconstruction. In the event of Ukraine’s accession to the European Union, the conditions under which agricultural support will be implemented, how existing support mechanisms will be transformed, and according to which criteria regional development funds will be distributed will be among the main topics of budget negotiations. However, the extent of the impact of enlargement on the budget will be shaped depending on membership conditions, transition periods, the structure of agricultural support, and future budget arrangements. In this respect, the preparations carried out by the European Commission within the scope of enlargement bring to the agenda the advance assessment of the financial burdens and changes in policy areas that may arise from the accession of new members and the restructuring of the Union’s financial structure in accordance with the enlargement process.
This process will also lead to financial priority differences between countries contributing to the Union budget and countries benefiting more from the budget becoming more pronounced. In this situation, net contributor countries will prioritize the effectiveness of budget expenditures and the preservation of fiscal discipline, while net beneficiary countries will attach importance to the continuation of existing support and the maintenance of economic convergence. In addition, increased competition for resources among agricultural support, regional development funds, and new strategic spending areas following enlargement may make it more complex to achieve budgetary compromise among member states. Moreover, priorities such as increasing defense expenditures, strengthening energy security, supporting digital transformation, and rebuilding Ukraine may place additional pressure on traditional budget items. Therefore, the financial sustainability of enlargement will depend not only on securing new resources but also on restructuring existing spending policies, increasing the effectiveness of financial support, and preserving financial solidarity among member states.
This interdependence between enlargement and institutional reform is also evident in the European Union’s migration and border security policies. The expanding geographical scope of the Union’s external borders requires the strengthening of common border management, asylum procedures, and security coordination in order to keep internal borders open to free movement. The Schengen system guarantees freedom of movement based on the removal of internal border controls while requiring the management of external borders according to common standards and the maintenance of mutual trust among member states. Therefore, border security has ceased to be an issue addressed solely within national jurisdictions and has become one of the European Union’s policy areas requiring common responsibility. The Migration and Asylum Pact, adopted in 2024 and beginning to be implemented as of June 12, 2026, aims to reorganize responsibility-sharing among member states, harmonize asylum procedures, and strengthen common capacity in external border management.
One of the fundamental elements of the Pact, the flexible solidarity mechanism, envisages supporting member states under migration pressure through relocation, financial contributions, or operational support from other members. This mechanism aims to reduce the unequal effects of migration movements on member states and strengthen the understanding of common responsibility. However, the ability of member states to fulfill their solidarity obligations in different forms may lead to debates concerning the scope and effectiveness of common responsibility in practice. Particularly where financial contributions can substitute for physical relocation obligations, the genuine nature of solidarity is questioned, deepening criticisms that this reduces migration management to merely a cost-balancing mechanism. Therefore, the success of the Pact is connected not only to strengthening border controls or accelerating asylum procedures, but also to establishing sustainable responsibility-sharing among member states and guaranteeing the rights of persons in need of international protection.
Another element gaining increasing importance in the European Union’s migration policy is the externalization of border management and strategic partnerships developed with third countries. This approach aims to manage irregular migration movements through cooperation with countries of origin and transit before they reach the borders of the European Union. Readmission agreements, border surveillance, combating human trafficking, financial support, and the development of migration management capacity are among the main components of the externalization policy. In this context, the European Union is deepening cooperation with neighboring and transit countries in order to manage migration movements and limit cross-border security threats. However, transferring migration management beyond the Union’s borders also brings significant problems concerning the scope of legal responsibilities, access to asylum applications, and the protection of fundamental rights. In particular, the implementation of safe third-country practices, accelerated border procedures, and return mechanisms must be assessed within the framework of the principle of non-refoulement and international protection obligations. The principle of non-refoulement, one of the fundamental principles of the 1951 Geneva Refugee Convention, prohibits the sending of persons to countries where their lives or freedoms are under threat and determines the legal limits of the European Union’s migration policies. Therefore, the externalization of migration must be evaluated not only in terms of operational efficiency and border security, but also in terms of the protection of human rights and compliance with international law. Therefore, the balance to be established between strengthening border security and protecting human rights is of decisive importance for both the European Union’s internal legitimacy and its international normative identity.
The transformation taking place in the European Union’s enlargement and border security policies also necessitates a reassessment of the relationship between the Union’s normative power identity and its capacity to act as a geopolitical actor. European integration historically developed as a political project aiming to exert influence in the international system through the institutionalization of principles such as democracy, human rights, the rule of law, and multilateral cooperation. Within this framework, enlargement policy has been used as a tool not only to create a stable and democratic political space around Europe, but also to support the economic and institutional transformation of candidate countries. However, the intensification of great power competition, the increase in regional conflicts, the transformation of energy dependencies into a strategic instrument, and competition over critical technologies have led the European Union to develop a more pronounced geopolitical approach in international relations.
Following the Russia-Ukraine War, strengthening security and defense capacity, diversifying energy supplies, reducing strategic economic dependencies, and improving foreign policy coordination have gained greater prominence among the Union’s priority policy areas. While these developments do not mean that the European Union has completely abandoned its normative identity, they point to a transformation requiring value-based foreign policy objectives and strategic interests to be managed within the same institutional framework. In particular, the increasing geopolitical importance of enlargement policy makes strategic assessments more influential in the membership processes of candidate countries while also making the consistent application of conditions concerning democracy, the rule of law, and fundamental rights more important. The European Commission explicitly emphasized in its 2025 enlargement approach that the advantages provided by gradual integration should depend on reform progress and the fulfillment of fundamental conditions such as the rule of law. In this context, the European Union’s strengthening as a geopolitical actor depends not only on increasing its economic and military capacity, but also on the extent to which it can preserve its normative principles in its foreign policy practices.
The enlargement, institutional reform, financial sustainability, and border security problems facing the European Union stand out not as independent developments from one another, but as interdependent dynamics shaping the future of integration. Enlargement has the potential to expand the Union’s geographical and geopolitical sphere of influence, while also bringing to the agenda the restructuring of existing institutional mechanisms, the distribution of financial resources, and the common political framework. Gradual integration offers a flexible model that can enable candidate countries to participate in the Union’s economic and institutional structure at earlier stages, while carrying risks such as different levels of participation becoming permanent and the ultimate membership perspective becoming uncertain. Similarly, expanding qualified majority voting and restructuring the Commission have the potential to increase decision-making capacity, but may also raise new debates concerning the national competences of member states and institutional trust.
In the financial sphere, the resource needs created by enlargement will bring the reassessment of traditional spending areas such as the Common Agricultural Policy and Cohesion Policy to the agenda, while common responsibility mechanisms in the field of migration and border security and strengthened cooperation with third countries are gaining importance. In this framework, the future of the European Union depends not only on the speed of enlargement or the increase in the number of members, but also on reconciling different national priorities around common objectives, developing institutional capacity, and maintaining financial solidarity. Therefore, the fundamental issue facing the Union is to establish the institutional and political conditions under which the two processes can support each other, rather than making a definitive choice between enlargement and deepening. The sustainability of the future integration model will depend on maintaining a credible membership perspective, the effectiveness of decision-making processes, financial solidarity, and the conduct of security policies in accordance with fundamental rights.
