INTRODUCTION
The security and defense of the European Union represent one of the most dynamic dimensions of the European project. Since the inception of the idea of a European community in the mid-20th century, ensuring and maintaining Europe’s own security has been a constant concern for political decision-makers at the European level.
The concept of the European Security and Defence Policy (ESDP) took shape at the Cologne European Council (June 1999), in the period following the Kosovo conflict and subsequent to the Franco-British agreement of St. Malo (December 1998). In essence, the ESDP aimed at developing an autonomous decision-making capacity and, when the North Atlantic Alliance (NATO) as a whole is not engaged, at launching and coordinating EU-led military operations in response to crisis situations — with the commitment of national resources by Member States based on sovereign decisions.
Especially after the September 11, 2001 terrorist attacks on New York’s Twin Towers, given the evolution of the international environment following the adoption of the ESDP Global Objective in 1999, the emergence of asymmetric threats, and the EU’s goal of asserting itself as an international actor, it became increasingly necessary to expand the Union’s field of action. This expansion required “the shaping of a common European perception of international risks, a shared political will to use existing capabilities, and a joint decision to enhance those capabilities” [1].
FROM THE EUROPEAN SECURITY STRATEGY TO THE TREATY OF LISBON
The European Security Strategy, adopted in December 2003 under the title “A Secure Europe in a Better World”, represented a genuine milestone in the consolidation of the European Union’s Common Foreign and Security Policy (CFSP) [2]. The document provided the Union with a coherent conceptual framework for defining its global role, setting clear strategic objectives in the field of security, and guiding the collective action of the Member States toward more proactive, rapid, and integrated responses to the challenges of the international environment [3].
Through this strategy, the European Union identified the main multidimensional threats to international order — global terrorism, the proliferation of weapons of mass destruction, regional conflicts, and transnational organized crime — and emphasized the pressing need to develop a “European strategic culture” grounded in cooperation, solidarity, and shared responsibility in matters of security and defence.
Thus, the 2003 Strategy marked the transition from a reactive to a preventive policy, strengthening the European Union’s profile as a global strategic actor, capable of acting autonomously or in cooperation with its international partners, depending on the nature of the threats and the specific geopolitical context [5].
Through the Treaty of Lisbon (which entered into force on 1 December 2009), the Common Security and Defence Policy (CSDP) of the European Union replaced the former European Security and Defence Policy (ESDP), marking a decisive stage in the institutionalization of the Union’s defence dimension. The Treaty modified both the name and the legal structure of this policy, granting it a distinct section under Title V of the Treaty on European Union (TEU), thereby underscoring the importance and specificity of the CSDP as an essential pillar of the Common Foreign and Security Policy (CFSP).
In addition to the formal recognition of the CSDP, the Treaty of Lisbon introduced a series of innovative provisions designed to support the progressive development of a common European defence policy, with the potential to evolve into a common defence of the Union, in accordance with Article 42(2) TEU. The main innovations include [4]:
1. the mutual assistance clause (Article 42(7) TEU), which obliges Member States to provide aid and assistance to another Member State subject to armed aggression, in the spirit of European solidarity;
2. the solidarity clause (Article 222 TFEU), under which the Union and the Member States act jointly in the event of terrorist attacks or natural or man-made disasters;
3. the strengthening of the role of the European Defence Agency (EDA), established in 2004 to support the development of defence capabilities, technological research, and industrial cooperation in the defence sector;
4. the establishment of Permanent Structured Cooperation (PESCO), which allows Member States with more advanced military capabilities to collaborate within a stable legal framework for the joint development of capabilities and operational planning.
Although the Treaty strengthened the normative framework of the CSDP, its intergovernmental nature was preserved. Major decisions continue to be taken by the Council of the European Union, generally by unanimity, while the funding and operational means of missions conducted under the CSDP are provided by the Member States, in line with the principles of solidarity and burden sharing.
In essence, the CSDP provides the Union with a functional framework for conducting operational missions in third countries, aimed at maintaining peace, preventing conflicts, and strengthening international security. These operations — whether civilian or military — rely on the resources made available by the Member States, demonstrating the Union’s capacity to act in concert in support of regional and global stability [6].
THE WAR IN UKRAINE AND THE EUROPEAN UNION’S COMMON SECURITY AND DEFENCE POLICY
Since 2022, the unprovoked invasion of Ukraine by the Russian Federation has triggered a paradigm shift in the European Union’s perception of the international security environment. This act of aggression marked the end of the post–Cold War era, prompting a profound strategic reassessment of threats to the European continent and an unprecedented acceleration of the Union’s military and strategic consolidation [8].
Just one month after the outbreak of the Russian Federation’s invasion of Ukraine, the foreign and defence ministers of the European Union Member States adopted, on 10 March 2022 in Brussels, the document entitled “A Strategic Compass for Security and Defence” — a major initiative marking the Union’s transition towards a more coherent, operational, and autonomous common defence policy. The adoption of the Compass took place in a context of unprecedented geopolitical tension, defined by the return of war to the European continent and the need to redefine the Union’s security architecture [9].
The Strategic Compass sets out a series of concrete objectives designed to strengthen the Union’s ability to act rapidly and effectively in crisis situations, including the establishment of an EU Rapid Deployment Capacity of up to 5,000 troops, as well as the reinforcement of operational cooperation, resilience, and strategic partnerships [10]. The document provides a shared vision of threats and outlines the means through which the Union can become a credible security provider, capable of protecting its citizens, values, and interests, while also contributing actively to international peace and stability [11].
In its preamble, the Council of the European Union emphasizes that the Compass constitutes the Union’s “strategic response to a changing world,” drafted at a time when Russia’s unjustified and unprovoked war of aggression against Ukraine has exposed Europe’s vulnerabilities in the fields of security and defence. The Compass therefore represents a ten-year action plan aimed at strengthening the Union’s strategic autonomy, not by undermining its complementarity with NATO, but rather by enhancing cooperation with the Alliance, with global partners, and with the EU’s eastern neighbourhood [8].
Consequently, the Strategic Compass marks a historic turning point in European defence policy, reaffirming the Member States’ commitment to building a stronger, more united, and more resilient Union, better equipped to respond to emerging threats in an increasingly volatile geopolitical environment.
The cooperation between the European Union and NATO has undergone significant consolidation with the signing of the new EU-NATO Joint Declaration on 10 January 2023, at the Alliance’s headquarters in Brussels. This document represents the third joint declaration adopted by the two organizations - following the Warsaw Declaration (2016) and the Brussels Declaration (2018) - and forms part of a strategic partnership that has evolved over more than two decades. The new declaration reaffirms the shared commitment of both organizations to transatlantic security, emphasizing the need for a unified and complementary approach in addressing the complex, multidimensional threats of the current geopolitical environment [12].
The document’s most notable innovation lies in its expression of a “commitment to further strengthening cooperation” between the European Union and NATO, both through the deepening of existing areas of collaboration and through the expansion into new strategic domains. These include global geostrategic competitiveness, democratic resilience, the protection of critical infrastructure, the management of disruptive technologies, space security, and the security implications of climate change. Furthermore, particular attention is devoted to combating disinformation campaigns, information manipulation, and foreign interference in the internal political processes of Member States [13].
The 2023 Joint Declaration reflects an increasingly pronounced convergence between the EU and NATO in their strategic vision of collective defence and global security. However, parts of the academic literature warn of the potential institutional overlap and the erosion of European strategic autonomy, especially given that NATO continues to hold primacy in collective defence matters [14]. Analysts such as Sven Biscop and Jolyon Howorth emphasize the need to maintain a functional balance between complementarity and autonomy, allowing the EU to develop its own defence capabilities without fostering structural dependency on the Alliance [15].
In this context, the European Parliament Resolution of 2 April 2025 on the implementation of the Common Security and Defence Policy (CSDP) – Annual Report 2024 emphasizes that Russia’s war of aggression against Ukraine constitutes “the most serious and unprecedented threat to world peace and European security” and that, for the first time in decades, the European Union faces a direct existential threat to its values, institutions, and external borders [7].
This new geopolitical reality has led the Union to reorient its defence priorities, strengthen its strategic autonomy, and integrate military and economic instruments within its overall security architecture. Moreover, it has driven the adoption of key structural initiatives, such as the European Defence Industrial Strategy (EDIS) and the “ReArm Europe” Plan (2025), aimed at ensuring the resilience, responsiveness, and military interoperability of the Member States.
Consequently, Russia’s aggression has not only redefined the nature of external threats but has also accelerated the transformation of the European Union from a normative actor into a geopolitical power, endowed with the capacity for deterrence and collective defence on a continental scale.
The war in Ukraine has acted as a genuine catalyst for European integration in the field of defence, compelling the European Union to adopt a more coherent and ambitious approach to strengthening its defence capabilities. In this regard, the European Parliament Resolution of April 2025 on the implementation of the Common Security and Defence Policy highlights several structural advancements that reflect the Union’s transition toward a collective security and defence strategy.
The resolution emphasizes in particular the following initiatives:
5. The European Peace Facility (EPF), which enables the financing of military equipment deliveries to Ukraine, marking the first use of EU funds to directly support a state under external aggression [16];
6. The ASAP (Act in Support of Ammunition Production) [17] and EDIRPA (European Defence Industry Reinforcement through Common Procurement Act) regulations, both adopted in 2023, designed to increase Europe’s ammunition production capacity, facilitate joint public procurement, and reduce dependence on external suppliers [18];
7. The European Defence Industrial Strategy (EDIS) and the European Defence Industry Programme (EDIP), launched in 2024, aimed at strengthening the European Defence Technological and Industrial Base (EDTIB) and achieving genuine strategic autonomy through innovation, cooperation, and collective investment [19].
Taken together, these initiatives represent a paradigm shift in the European Union’s security posture — from a primarily civilian and diplomatic approach, focused on crisis management, to a more integrated military approach, centred on deterrence, collective defence, and the projection of stability in its strategic neighbourhood. This transformation demonstrates both the maturation of the CSDP and the European Union’s ambition to act as an autonomous and credible geopolitical actor in the evolving international order.
The Resolution reaffirms the complementary nature of the relationship between the European Union and NATO, emphasizing that “a stronger and more capable European Union in the field of defence will make a positive contribution to global and transatlantic security.” This statement reflects the strategic vision of synergistic cooperation between the two organizations, grounded in the principles of solidarity and interoperability in the face of common threats [7].
At the same time, the European Parliament underscores the importance of operationalizing Article 42(7) of the Treaty on European Union (TEU), which provides for mutual assistance among Member States in the event of armed aggression. This article is regarded as the legal cornerstone of European military solidarity, applicable even to traditionally neutral states, thereby strengthening the strategic unity and defensive cohesion of the Union.
Furthermore, the document advocates for the development of a European pillar within NATO, intended to enhance the Union’s contribution to transatlantic security and reduce structural dependencies. This pillar would be built upon the development of joint military capabilities in key areas such as air and missile defence, electronic warfare, hypersonic systems, and cyber defence — elements considered vital for credible and effective deterrence against emerging strategic threats.
Thus, the Resolution advances a vision of EU–NATO strategic co-evolution, in which European strategic autonomy is not conceived as an alternative to the Alliance but rather as a reinforcing component of the European defence pillar, thereby contributing to collective security and global stability.
The European Parliament calls for the provision of “decisive and timely” military assistance to Ukraine, emphasizing the importance of delivering fighter aircraft, drones, air defence systems, and ammunition as part of a collective effort to strengthen the country’s defensive capabilities and strategic resilience [7]. The resolution underlines that this military support must be coordinated, sustainable, and long-term in nature, enabling Ukraine not only to withstand ongoing Russian aggression but also to deter any future acts of destabilization by the Russian Federation.
In this context, the “Porcupine Strategy” initiative, referenced in the European Defence White Paper – Readiness 2030, articulates the Union’s objective of transforming Ukraine into a well-fortified and resilient state, capable of effectively deterring any form of external aggression. The concept rests on the idea of developing a layered defence posture, integrating mobility, advanced technology, and international cooperation, thereby making any potential attack prohibitively costly and strategically unsustainable for an aggressor [20].
Furthermore, the resolution highlights the importance of the Kyiv Security Compact and the bilateral security commitments concluded between Ukraine and several EU Member States, as part of a broader international framework of security guarantees [21]. These agreements represent a critical step toward the institutionalization of European defence assistance and the construction of a sustainable European security architecture, founded on partnership, solidarity, and collective defence [22].
CONCLUSIONS
The European Parliament’s 2025 Resolution marks a genuine turning point in the evolution of the Common Security and Defence Policy [7], signalling a shift from a largely symbolic framework, characterized by limited civilian missions and modest operational ambitions, to a comprehensive and integrated defence strategy built upon coordinated industrial investment, military interoperability, and strategic solidarity among Member States.
The Russian Federation’s war of aggression against Ukraine has acted as a catalyst for the deep transformation of the CSDP, accelerating the emergence of a genuine European Defence Union [23]. This process redefines the concept of collective sovereignty within the Union, moving beyond traditional intergovernmental cooperation toward a shared vision of European defence, grounded in mutual responsibility and strategic autonomy [24].
For the first time in its history, the European Union assumes an active geopolitical role, oriented toward the “defence of peace through strength”- a concept that encapsulates the political and strategic maturation of the European project [25]. Through this renewed posture, the EU is no longer confined to the role of a normative actor, but emerges as a credible guarantor of the rules-based international order, reaffirming its commitment to democratic values, international law, and the principle of collective solidarity.