The EU's Mutual Defence Clause: Legal and Strategic Considerations on Article 42(7) TEU in an Age of Renewed Military Threats

Federica Fazio No. 4/2025 Working Paper Series The EU’s Mutual Defence Clause: Legal and Strategic Considerations on Article 42(7) TEU in an Age of Renewed Military Threats THE EU’s MUTUAL DEFENCE CLAUSE: LEGAL AND STRATEGIC CONSIDERATIONS ON ARTICLE42(7) TEU IN AN AGE OF RENEWED MILITARY THREATS FEDERICA FAZIO * EU institutions have expanded their involvement in defence since 2016, prompted by Brexit and Donald Trump’s first presidential victory. This trend has become even more pronounced since the 2022 Russian invasion of Ukraine. NATO remains central to Europe’s territorial defence, as evidenced by Finland and Sweden’s accession, yet there also exists a legal basis for the EU to play a role. Article 42(7) of the Treaty on European Union (TEU) obliges Member States to assist each other in the event of armed aggression, echoing Article 5 of the North Atlantic Treaty (NAT). This provision has received limited attention from legal scholars. With the war in Ukraine intensifying, concerns over Trump undermining Article 5 NAT and rising risks of military and hybrid attacks on Europe, it is crucial to understand how the EU’s mutual defence clause would be implemented. This includes its interplay with the EU’s solidarity clause in Article 222 of the Treaty on the Functioning of the EU (TFEU) and NATO’s own mutual defence clause. To this end, this article undertakes a legal and strategic analysis of Article42(7)TEU. Following an introduction that outlines the topic and methodology, Section 1 offers a legal perspective, while Section 2 a strategic perspective. Section 3 concludes that, while significant progress has been made, the EU is not yet in a position to credibly threaten the use of force in the exercise of collective defence. INTRODUCTION In 1991, then-Belgian Minister of Foreign Affairs, Mark Eyskens, described the EU as ‘an economic giant, a political dwarf and a military worm’.1 Today, the EU is no longer a political dwarf or a military worm, though military capability shortfalls remain. 1* PhD Candidate in the School of Law and Government at Dublin City University (DCU) and Academic Assistant in the European Legal Studies Department at the College of Europe in Bruges. The author is deeply grateful to Prof Federico Fabbrini and Dr Kenneth McDonagh at DCU, for their invaluable insights and guidance in the development of this article, as well as to Prof Ben Tonra at University College Dublin for his insightful comments and continued support. The author would also like to thank Prof Michal Onderco and Drs Daniel Fiott, Joris Larik, Eva Kassoti, Narin Idriz and Niels Kirst for their helpful comments, and Drs Alezini Loxa and Annegret Engel, Editors-in-Chief of the Nordic Journal of European Law, where this article was published on 27 October 2025, for her interest in this topic and kind assistance throughout the review process. Part of this paper was presented at the PhD workshop ‘The legal implications of the EU’s geopolitical awakening’, jointly organised by the Asser Institute’s Centre for the Law of EU External Relations (CLEER) and Leiden University College The Hague on 14-15 November 2024. It was subsequently published as a Working Paper in an edited volume of the same name in the CLEER paper series in March 2025. As quoted by Craig R Whitney, ‘War in the Gulf: Europe; Gulf Fighting Shatters Europeans’ Fragile Unity’, (The New York Times, 25 January 1991) <https://www.nytimes.com/1991/01/25/world/war-in-the-gulf-europe-gulf-fighting-shatters-europeans-fra gile-unity.html> accessed 20 September 2024. In 2007, the Lisbon Treaty modified the 1992 Maastricht Treaty (or TEU) – as well as the other founding treaty, the Treaty Establishing the European Community (TEC), which it renamed as TFEU – and transformed the European Security and Defence Policy (ESDP), establishing the Common Security and Defence Policy (CSDP). Outlined in Articles 42-46 of Title V, Section 2, the CSDP has made security and defence an integral part of the Common Foreign and Security Policy (CFSP) intergovernmental framework and allows EU Member States to make security and defence policy decisions on the basis of unanimity.2 While reaffirming the Maastricht Treaty’s principle that a common defence policy would develop progressively, with a common defence requiring unanimous agreement by the European Council,3 the Lisbon Treaty introduced a mutual assistance obligation for EUMember States in Article 42(7) TEU. This obligation requires Member States to assist one another in the event of an armed aggression. Consequently, although the failure of the 1952 European Defence Community project means that the EU lacks a common defence – such as NATO’s integrated military command structure, shared nuclear doctrine, and other traditional defensive alliance characteristics – the EU Treaty now includes a qualified mutual defence clause. Despite acknowledging that NATO remains the cornerstone of territorial defence for those countries who are members of both organisations, the 2016 EU Global Strategy and, more recently, the 2022 Strategic Compass, have stressed the need for EU Member States to be prepared to translate mutual assistance commitments into action.4 The strategic autonomy envisaged in 2016 remains largely a work in progress, as highlighted by the continued need to negotiate and align with the US, exemplified by the EU-US Framework on Reciprocal, Fair, and Balanced Trade announced in August.5 Yet, the EU has clearly made considerable steps forward, particularly since Russia launched an all-out war against Ukraine on 24 February 2022.6 The Union has supplied Ukraine with €11.1 billion in military aid through the European Peace Facility (EPF), an off-budget fund which enabled it to provide lethal 6 See, e.g., Federico Fabbrini, ‘To “Provide for the Common Defence”: Developments in Foreign Affairs and Defence’ in Federico Fabbrini (ed), The EU Constitution in Time of War (Oxford University Press, 2025) 21–47; Daniel Fiott, ‘In every crisis an opportunity? European Union integration in defence and the War on Ukraine’ (2023) 45(3) Journal of European Integration 447. 5 Europea Commission, ‘Joint Statement on a United States-European Union framework on an agreement on reciprocal, fair and balanced trade’, Statement, (21 August 2025), available <https://policy.trade.ec.europa.eu/news/joint-statement-united-states-european-union-framework-agreemen t-reciprocal-fair-and-balanced-trade-2025-08-21_en> accessed 23 September 2025. 4 European External Action Service, ‘Shared Vision, Common Action: A Stronger Europe: A Global Strategy for the European Union’s Foreign and Security Policy’ (June 2016) (EUGS) 9, 14, 19 and 20 <https://www.eeas.europa.eu/sites/default/files/eugs_review_web_0.pdf> accessed 20 September 2024; European External Action Service, ‘A Strategic Compass for Security and Defence. For a European Union that protects its citizens, values and interests and contributes to international peace and security’ (March 2022) 10, 14, 23, 28, 30, 31, 34, 35, 36, 39, 40, 53 and 54, <https://www.eeas.europa.eu/sites/default/files/documents/strategic_compass_en3_web.pdf> accessed 20 September 2024. 3 Ibid Article 42(2); Treaty on European Union [1992] OJ C191/59 Article J.4(1). 2 Consolidated version of the Treaty on European Union [2016] OJ C 202/38 (TEU) Article 42(4). weapons for the first time,7 and launched a training mission for Ukrainian forces on its soil, another first.8 The EU has also introduced initiatives like the European Defence Industry Reinforcement through common Procurement Act (EDIRPA)9 to address capability gaps, the Act in Support of Ammunition Production (ASAP)10 to boost artillery shell production, the European Defence Industry Strategy (EDIS),11 its first defence industrial strategy, supported by the European Defence Industry Programme (EDIP)12 for long-term readiness, and, more recently, the ReArm Europe Plan/Readiness 203013 to facilitate national defence budget increases. Additionally, the Strategic Compass envisions the creation of a Rapid Deployment Capacity (RDC) of 5,000 troops by 2025.14 Therefore, the EU has adopted important defence initiatives and, by endangering the credibility of NATO’s Article 5 security guarantee, the second Trump administration is likely to accelerate this trend further. In light of these developments, this article aims to review the EU’s mutual assistance 14 EEAS, ‘A Strategic Compass for Security and Defence’ (n4) 6, 11, 25, and 31. 13 European Commission, ‘Letter by President von der Leyen on defence’ (4 March 2025) <https://ec.europa.eu/commission/presscorner/api/files/attachment/880628/Letter%20by%20President% 20von%20der%20Leyen%20on%20defence.pdf> accessed 20 September 2024; see also European Commission, ‘Communication from the Commission Accommodating increased defence expenditure within the Stability and Growth Pact’ C(2025) 2000 final (19 March 2025) <https://defence-industry-space.ec.europa.eu/document/download/a57304ce-1a98-4a2c-aed5-36485884f1a 0_en?filename=Communication-on-the-national-escape-clause.pdf> accessed 7 April 2025; European Commission, ‘Proposal for a Council Regulation establishing the Security Action for Europe (SAFE) through the reinforcement of European defence industry Instrument’ COM(2025) 122 final (19 March 2025) <https://defence-industry-space.ec.europa.eu/document/download/6d6f889c-e58d-4caa-8f3b-8b93154fe20 6_en?filename=SAFE%20Regulation.pdf> accessed 7 April 2025. 12 European Commission, ‘Proposal for a Regulation of the European Parliament and of the Council establishing the European Defence Industry Programme and a framework of measures to ensure the timely availability and supply of defence products (‘EDIP’)’ COM(2024) 150 final (5 March 2024)<https://defence-industry-space.ec.europa.eu/document/download/6cd3b158-d11a-4ac4-8298-91491e 5fa424_en?filename=EDIP%20Proposal%20for%20a%20Regulation.pdf> accessed 20 September 2024. 11 European Commission, ‘Joint Communication to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions A New European Defence Industrial Strategy: Achieving EU Readiness Through a Responsive and Resilient European Defence Industry’ JOIN(2024) 10 final (5 March 2024) <https://defence-industry-space.ec.europa.eu/document/download/643c4a00-0da9-4768-83cd-a5628f5c306 3_en?filename=EDIS%20Joint%20Communication.pdf> accessed 20 September 2024. 10 European Commission, ‘Commission Implementing Decision of 18.10.2023 on the Financing of the Instrument on Supporting Ammunition Production (ASAP) Established by Regulation (EU) 2023/1525 of the European Parliament and of the Council and the Adoption of the Work Programme for 2023-2025’ C(2023) 7320 final <https://defence-industry-space.ec.europa.eu/document/download/5845b34d-bb2f-4381-aca3-ec9ff965f68 7_en?filename=C_2023_7320_1_EN_ACT_and_annex.pdf> accessed 20 September 2024. 9 European Commission, ‘Commission Implementing Decision of 15.3.2024 on the Financing of the Instrument for the Reinforcement of the European Defence Industry through Common Procurement (EDIRPA) Established by Regulation (EU) 2023/2418 of the European Parliament and of the Council and the Adoption of the Work Programme for 2024-2025’ C(2024) 1700 final <https://defence-industry-space.ec.europa.eu/document/download/8b38112b-a9e2-499e-bb1e-b8dbfc6dfb 27_en?filename=EDIRPA%20Implementing%20Decision%20EN.pdf> accessed 20 September 2024. 8 Council of the EU, ‘Ukraine: EU launches Military Assistance Mission’ (Press Release, 15 November 2022) <https://www.consilium.europa.eu/en/press/press-releases/2022/11/15/ukraine-eu-launches-military-assist ance-mission> accessed 20 September 2024. 7 Council of the EU, ‘European Peace Facility: Timeline – European Peace Facility’ (Last review: 4 December 2024) <https://www.consilium.europa.eu/en/policies/european-peace-facility/> accessed 7 January 2025; see also Federico Fabbrini, ‘Funding the War in Ukraine, the European Peace Facility, the Macro-Financial Assistance Instrument, and the Slow Rise of and EU Fiscal Capacity’ (2023) 11(4) Politics & Governance 52. clause, enshrined in Article 42(7) TEU, using a law-in-context approach.15 The article is structured as follows. The next Section provides a legal analysis of Article 42(7) TEU and the collective defence responsibilities it entails for EU members, including differences and overlaps with similar obligations under Article 222 TFEU and Article 5 NAT. The legal analysis shows that, similarly to Article 5 NAT, Article 42(7) TEU envisages an obligation of result, not of means but no disciplinary measures are contemplated in the event of inaction or inadequate action by one or more Member States. Furthermore, Article 42(7) TEU, like Article 5 NAT, covers both conventional and unconventional attacks – including cyber, hybrid, and space attacks, as well as state-sponsored and non-state sponsored terrorist attacks. This article, however, argues that the defence obligations triggered by the invocation of Article 42(7) TEU are automatic, unlike those under Article 5 NAT, but not, as some authors have suggested,16 unconditional, due to the presence of both the Irish and NATO clauses. The article concludes with a strategic analysis supporting a broad interpretation of Article 42(7) TEU, under whose scope both conventional and unconventional forms of aggression fall. To support this view, the article examines the EU’s latest security strategies – the 2016 EU Global Strategy (EUGS) and the 2022 Strategic Compass – along with their associated implementation strategies and progress reports. These documents reveal, however, that the EU has consistently prioritised asymmetric threats such as terrorism, cyberattacks, hybrid warfare and space-based risks while giving comparatively limited attention to conventional military threats. The fact that this remains the case despite Russia’s full-scale invasion of Ukraine suggests that NATO is likely to continue to serve as the primary framework for traditional collective defence in Europe. 2 LEGAL ANALYSIS OF ARTICLE 42(7) TEU Article 42(7) TEU states: If a Member State is the victim of armed aggression on its territory, the other Member States shall have towards it an obligation of aid and assistance by all the means in their power, in accordance with Article 51 of the United Nations Charter. This shall not prejudice the specific character of the security and defence policy of certain Member States. Commitments and cooperation in this area shall be consistent with commitments under the North Atlantic Treaty Organisation, which, for those States which are members of it, remains the foundation of their collective defence and the forum for its implementation.17 Several elements seem to deserve further examination: 17 TEU (n2) Article 42(7). 16 Hermann-Josef Blake and Stelio Mangiameli, ‘Article 42 [CSDP: Goals and Objectives; Mutual Defence] (ex-Article 17 TEU)’ in Hermann-Josef Blake and Stelio Mangiameli (eds), The Treaty on European Union (TEU): A Commentary (Berlin: Springer-Verlag Berlin Heidelberg 2013) 1228. 15 Megan Donaldson, ‘Peace, war, law: teaching international law in contexts’ (2022) 18(4) International Journal of Law in Context 393; Peter Cane, ‘Context, context everywhere’ (2020) 16(4) International Journal of Law in Context 459; William Twinning, Law in Context: Enlarging a Discipline (Oxford University Press, 1997). I. The use of the words ‘armed aggression’ rather than ‘armed attack’; II. The fact that the aggression must have taken place on the territory of the aggressed; III. The framework of response: bilateral (Member States) vs collective (EU); IV. The phrasing ‘obligation of aid and assistance by all the means in their power’; V. The express reference to Article 51 of the Charter of the United Nations (UNC); VI. The so-called ‘Irish formula’; VII. The ‘NATO formula’. 1.1 ARMED AGGRESSION VS ARMED ATTACK An armed attack is a form of armed aggression, which means that armed aggression is a broader category, comprising other forms of aggression beyond armed attacks.18 Although the two terms are often used interchangeably, some authors19 have argued that since Article 42(7) TEU refers to armed aggression while Article 5 NAT to armed attack, the former could potentially cover a broader spectrum of threats than the latter.20 For example, it could be activated for those hybrid acts that do not meet the threshold of armed attack under Article 5 NAT,21 such as recent incidents in the Baltic Sea.22 Therefore, at least in theory, EU Member States would be legally bound to collective defence in cases when NATO Allies are not. This argument seems implausible for two reasons. 22 For an overview of recent incidents in the Baltic Sea, see Reuters, ‘Recent suspected underwater sabotage incidents in the Baltic Sea’, (21 February 2025), available <https://www.reuters.com/world/europe/recent-suspected-underwater-sabotage-incidents-baltic-sea-2024-1 2-03/> accessed 15 March 2025; German Federal Foreign Office, ‘Joint Declaration by the Foreign Ministers of Germany, France, Poland, Italy, Spain and the United Kingdom in Warsaw’ (Press Release, 19 November 2024) <https://www.auswaertiges-amt.de/en/newsroom/news/2685538-2685538> accessed 7 December 2025; European Commission, ‘Joint Statement by the European Commission and the High Representative on the Investigation into Damaged Electricity and Data Cables in the Baltic Sea’ (Statement, 26 December 2024) <https://ec.europa.eu/commission/presscorner/detail/en/statement_24_6582> accessed 7 January 2025; Statsministeriet, ‘Joint Statement of the Baltic Sea NATO Allies’, (14 January 2025), available <https://stm.dk/media/ndolltur/joint-statement-of-the-baltic-sea-nato-allies-summit.pdf> accessed 7 January 2025. 21 As Perot pointed out, ‘when it comes to how to react to the most serious forms of hybrid threats, the general idea that emerged […] was that of a division of labor between the EU and NATO, whereby the EU would be responsible for responding first through Article 222 TFEU and then Article 42.7 TEU, while NATO would be called upon to intervene in the event of further escalation, on the basis of its own collective defense clause’. See Elie Perot, ‘The European Union’s nascent role in the field of collective defense: between deliberate and emergent strategy (2024) 46(1) Journal of European Integration, 11; see also Aurel Sari, ‘The Mutual Assistance Clauses of the North Atlantic and EU Treaties: The Challenge of Hybrid Threats’ (2019) 10 Harvard National Security Journal 405, 452 and 455. Additionally, Sari has argued that, by covering terrorist attacks and man-made disasters, Article 222 TFEU gives EU Member States legal basis to assist one another in responding to acts of sabotage that fall below the threshold of an armed attack or armed aggression and, therefore, do not trigger Article 5 NAT or Article 42(7) TEU; Ibid 458 and 459. 20 See e.g. Jean-Christophe Martin, ‘La Clause de Défense Mutuelle’ in Elsa Bernard, Quentin Loïez and Stéphane Rodrigues (eds), L’Union européenne de la défense : commentaire article par article (Bruylant 2024) 408. 19 Anne Bakker et al, ‘The EU’s Mutual Assistance Clause: Spearheading European Defence: Employing the Lisbon Treaty for a Stronger CSDP’ (2016) Report, Clingendael, 25 <https://www.jstor.org/stable/resrep05543.8?seq=1> accessed 16 October 2024. 18 See e.g. Federica Fazio, ‘Collective defence in NATO: A legal and strategic analysis of Article 5 in light of the war in Ukraine’ (5 November 2024) DELI Working Paper Series 2/24, Dublin European Law Institute, 6 <https://zenodo.org/records/14037328> accessed 18 November 2025. First, it is not only Article 5 NAT that preferred the coinage armed attack to armed aggression but also Article 51 UNC, which both Article 5 NAT and 42(7) TEU make express reference to.23 As pointed out by Reichard, Article 103 UNC gives it legal primacy over other international treaties.24 Article 30(1) of the Vienna Convention on the Law of Treaties (VCLT) reflects the effects of this supremacy.25 In light of this, and pursuant to the duty of consistent interpretation of EU law with international law – which stems from Articles 3(5) and 21(1) TEU and has been recognised by the Court of Justice of the EU (CJEU) in cases such as Poulsen (C‑286/90)26 and Air Transport Association of America (C‑366/10)27 – it follows that Article 42(7) TEU should, insofar as possible, be interpreted in conformity with Article51 UNC. Accordingly, the term ‘armed aggression’ in Article 42(7) TEU should be understood as synonymous with ‘armed attack’ under Article 51 UNC.28 In the absence of any reference to the motives behind the change in wording from armed attack into armed aggression in the documents that were issued by the European Convention and formalised by the Intergovernmental Conference of the Representatives of the Governments of the Member States between December 2002 and April 2003, it is safe to assume, as some commentators have, that ‘the reference to “armed aggression” may simply be the result of a literal translation of the French “agression armée”’.29 Second, in 2016, NATO Allies recognised cyberspace as a domain of warfare, alongside land, sea, air and, more recently, space, and countering hybrid threats has been an area of strengthened EU-NATO cooperation ever since.30 Additionally, ‘[h]ybrid attacks have been explicitly identified by both the EU Strategic Compass and the NATO Strategic Concept as qualifying for collective response’.31 Furthermore, earlier this year, NATO 31 Bernard Siman, ‘Hybrid Warfare: Attribution is Key to Deterrence’ (Egmont Institute, 30 January 2023) <https://www.egmontinstitute.be/hybrid-warfare-attribution-is-key-to-deterrence/> accessed 10 October 2024. Already in 2016, the Joint Framework on countering hybrid threats stated that ‘if multiple serious hybrid threats constitute armed aggression against an EU Member State, Article 42 (7) TEU could be invoked to provide an appropriate and timely response. A wide-ranging and serious manifestation of hybrid threats may also require increased cooperation and coordination with NATO’. See European Commission, ‘Joint Communication to the European Parliament and the Council-Joint Framework on countering hybrid threats’ JOIN(2016) 18 final (6 April 30 European Parliament, ‘Joint Declaration by the President of the European Council, the President of the European Commission and the Secretary General of the North Atlantic Treaty Organization’ (8 July 2016) <https://www.europarl.europa.eu/cmsdata/121580/20160708_160708-joint-NATO-EU-declaration.pdf> accessed 20 September 2024. 29 Bob Deen, Dick Zandee, and Adája Stoetman, ‘Uncharted and uncomfortable in European defence: The EU’s mutual assistance clause of Article 42(7)’ (January 2022) Report, Clingendael, 7 <https://www.clingendael.org/sites/default/files/2022-01/uncharted-and-uncomfortable.pdf> accessed 20 September 2024; see also Jolyon Howorth, ‘The European Draft Constitutional Treaty and the Future of the European Defence Initiative: A Question of Flexibility’ (2004) 9(4) European Affairs Review 483; Elie Perot ‘The art of commitments: NATO, the EU, and the interplay between law and politics within Europe’s collective defence architecture’ (2019) 28(1) European Security 40, 45; Martin (n20) 408; Sari (n21) 418. 28 Blake and Mangiameli (n16) 122; Martin (n20) 408-409. 27 Case C-366/10 Air Transport Association of America and Others v Secretary of State for Energy and Climate Change EU:C:2011:864 paras 101, 103, and 109. 26 Case C-286/90 Poulsen and Diva Navigation EU:C:1992:453 paras 9 and 10. 25 See, e.g. Alexander Orakhelashvili, ‘1969 Vienna Convention. Article 30: Application of Successive Treaties Relating to the Same Subject Matter’ in Olivier Corten and Pierre Klein (eds), The Vienna Convention on the Law of Treaties A Commentary (Oxford University Press, 2011) 764 and 780. 24 Martin Reichard, ‘Collective Self-Defence’ in Martin Reichard (ed), The EU-NATO Relationship: A Legal and Political Perspective (Routledge 2006) 210. 23 Fazio, ‘Collective defence in NATO’ (n18) 5. announced the launch of Baltic Sentry to bolster its military presence in the Baltic Sea and deter further sabotage of critical undersea infrastructure by state and non-state actors alike.32 Therefore, it seems unreasonable to believe that an act of hybrid warfare would trigger Article42(7) TEU but not Article 5 NAT. Article 42(7) traces back to Article 4 of the Brussels Treaty (BT), which, like Article5NAT, was originally designed for collective defence against conventional military attacks, not attacks by non-state actors. The article’s activation in response to a non-state-sponsored terrorist attack, despite the existence of Article 222 TFEU (which is specifically designed to address such incidents), seems to support the argument of an extensive interpretation of this norm.33 Furthermore, like NATO, the EU recognised cyberspace and space as operational domains in 201834 and has since put forward a new Cybersecurity Strategy in 2020,35 a Military Vision and Strategy on Cyberspace as a Domain of Operations in 2021,36 the first-ever Space Strategy for Security and Defence in 2023,37 and the Space Act in 2025.38 As the strategic analysis section will show, there is a strong focus in the Compass on regular exercises to further strengthen mutual assistance in case of armed aggression, particularly in the cyber,39 hybrid,40 and space domains.41 Therefore, it seems safe to assume that, although the interpretation of Article 42(7) TEU has never been discussed or expanded in European Council decisions or conclusions, unlike that of Article 5 NAT in NATO Summit communiqués, Article 42(7) should be considered applicable under the same circumstances as Article 5. Non-traditional attacks, such as terrorist attacks, cyberattacks, 41 Ibid 34 and 36. 40 Ibid 31 and 39. 39 EEAS, ‘A Strategic Compass for Security and Defence’ (n4) 31, 35, and 39. 38 European Commission, Defence Industry and Space, ‘EU Space Act: Strengthening Safety, Resilience and Sustainability in Space’ (25 June 2025) <https://defence-industry-space.ec.europa.eu/eu-space-act_en> accessed 28 June 2025. 37 European Commission and High Representative of the Union for Foreign Affairs and Security Policy, ‘Joint Communication to the European Parliament and the CouncilEuropean Union Space Strategy For Security and Defence’ JOIN(2023) 9 final <https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52023JC0009> accessed 20 September 2024. 36 European External Action Service, ‘European Union Military Vision and Strategy on Cyberspace as a Domain of Operations’ EEAS(2021) 706 REV4 <https://www.statewatch.org/media/2879/eu-eeas-military-vision-cyberspace-2021-706-rev4.pdf> accessed 10 October 2025. 35 European Commission and High Representative of the Union for Foreign Affairs and Security Policy, ‘Joint Communication to the European Parliament and the Council - The EU's Cybersecurity Strategy for the Digital Decade’ JOIN(2020) 18 final <https://digital-strategy.ec.europa.eu/en/library/eus-cybersecurity-strategy-digital-decade-0> accessed 10 October 2025. 34 Council of the EU, ‘EU Cyber Defence Policy Framework’ (2018 update) 14413/18 (19 November 2018) <https://data.consilium.europa.eu/doc/document/ST-14413-2018-INIT/en/pdf> accessed 6 November 2025. 33 Blake and Mangiameli (n 16) 1225-1226; Martin (n20) 410-411. See also Section 1.3. 32 NATO, ‘Joint Press Conference by NATO Secretary General Mark Rutte with the President of Finland Alexander Stubb and the Prime Minister of Estonia Kristen Michal at the Baltic Sea NATO Allies Summit’ (14 January 2025) <https://www.nato.int/cps/en/natohq/opinions_232116.htm> accessed 20 September 2025; SHAPE, ‘Baltic Sentry to Enhance NATO's Presence in the Baltic Sea’ (14 January 2025) <https://shape.nato.int/news-releases/baltic-sentry-to-enhance-natos-presence-in-the-baltic-sea> accessed 10 February 2025. 2016)<https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex:52016JC0018> accessed 10 October 2024. hybrid attacks and attacks to, from and within space, are therefore also covered by the EU’s Article 42(7), with potential overlaps between the two clauses.42 1.2 ARMED AGGRESSION ON A MEMBER STATE’S TERRITORY While Article 5 NAT states that the armed attack against one or more NATO Allies must have been committed in ‘Europe or North America’, with Article 6 further clarifying the geographical reach of the attack that can trigger the mutual defence obligation, Article42(7)TEU simply states that a member state must be ‘victim of armed aggression on its territory’. This leads to two considerations: First, only the aggressed Member State(s) can invoke Article 42(7) TEU. It was France, the victim of the terrorist attacks, that invoked Article 42(7) in 2015. In contrast, in the case of Article 5 NAT, it was not the US, the victim of the terrorist attack, but its Allies who offered to invoke it.43 Second, in light of the fact that no further clarification is provided in terms of geographical coverage, overseas territories outside of Europe should be intended as included in the scope of Article 42(7). For example, should an attack occur on the land, in the waters or in the airspace of the French territory of La Martinique, in the Caribbean, France could potentially invoke Article 42(7) as it did after the Paris attacks. It could not invoke NATO’s Article 5 though, since the island is located below the Tropic of Cancer.44 However, it has been argued that since EU primary law does not apply to all overseas territories, neither should Article 42(7) TEU.45 In fact, some scholars and practitioners46 have analysed the distinction between the EU’s outermost regions (ORs), which include for example La Martinique, and the EU’s overseas countries and territories (OCTs). 46 See, e.g., Perot, ‘The art of commitments’ (n29) 49; Deen et al (n29) 17; Wessel Willem Geursen, Mapping the territorial scope of EU law (PhD thesis, Vrije Universiteit Amsterdam 2024) <https://research.vu.nl/ws/portalfiles/portal/307385687/ww%20geursenmapping%20the%20territorial%2 0scope%20of%20eu%20lawthesis%20including%20annexes%20-%2065e4818190907.pdf> accessed 18 February 2025. 45 Blake and Mangiameli (n16) 1226; see also Carmen-Cristina Cirlig, ‘The EU’s mutual assistance clause. First ever activation of Article 42(7) TEU’ (Briefing, European Parliamentary Research Service, 27 November 2015), 3 <https://www.europarl.europa.eu/thinktank/en/document/EPRS_BRI(2015)572799> accessed 10 November 2024. 44 Pol Navarro I Serradell, A Comparative Study of Article 5 of the NATO and Article 42(7) of the Treaty on the European Union: Its Scope and Limits (Finabel 2024) 12. 43 Fazio, ‘Collective defence in NATO’ (n18) 6. 42 Already in 2012, the European Parliament stated in its resolution on the EU’s mutual defence and solidarity clauses: political and operational dimensions that ‘[…] even non-armed attacks, for instance cyberattacks against critical infrastructure, that are launched with the aim of causing severe damage and disruption to a Member State and are identified as coming from an external entity could qualify for being covered by the clause’. See European Parliament, ‘European Parliament resolution of 22 November 2012 on the EU’s mutual defence and solidarity clauses: political and operational dimension (2012/2223(INI))’ P7 TA(2012)0456 para 13 <https://www.europarl.europa.eu/doceo/document/TA-7-2012-0456_EN.pdf> accessed 5 September 2024. As observed by Martin, following the Bataclan and Stade de France attacks, however, the EEAS further clarified that, to fall within the scope of Article 42(7) TEU and constitute armed aggression, ‘The attack must originate from abroad and its scope covers attacks by state and non-state actors [translated from French]’, as quoted in Martin (n20) 410-411; see also Sari (n21) 422. by the inclusion of the Irish and NATO clauses that follow, as their presence would be unnecessary if military means were not contemplated. Moreover, unlike the phrasing ‘as it deems necessary’ in Article 5 NAT, which grants Allies discretion over the nature, timing, and scale of their response,91 the wording ‘by all the means in their power’ in Article 42(7) TEU appears to allow far less flexibility.92 This has led some authors to argue that, unlike Article 5 NAT, Article 42(7) TEU ‘entails an unconditional obligation of mutual assistance’.93 Yet, the presence of the Irish and NATO clauses does pose conditions, as will be analysed in Sections 1.6 and 1.7. Therefore, much like NATO Allies, EU Member States are free to choose the type and scope of assistance. 1.5 THE EXPRESS REFERENCE TO ARTICLE 51 OF THE UNITED NATIONS CHARTER Like Article 5 NAT, Article 42(7) TEU makes express reference to Article 51 UNC. This reference was first introduced in Article 4 BT, and kept in Article 5 MBT and ArticleI-41(7)CT. This is because Article 51 UNC allows the members of the international community to act in both individual and collective self-defence in case of an armed attack directed against one of them, without previous authorisation by the UN Security Council. Both Article 5 NAT and Article 42(7) TEU are expressions of the right of collective defence and, therefore, the obligations they envisage must be consistent with Article 51 UNC.94 1.6 THE IRISH CLAUSE This clause did not form part of either Article 4 BT or Article 5 MBT. It first appeared in the Maastricht Treaty,95 primarily in response to Ireland’s concerns about neutrality, and later made its way into the collective defence clause with the draft CT and later the LT.96 Theprovision is generally understood to refer to militarily non-aligned Member States and countries with long-standing traditions of neutrality – currently Austria, Cyprus, Ireland and Malta – or special security and defence arrangements – such as those with Denmark, which until 2022 had an opt-out from the CSDP.97 The clause no longer applies to Finland and Sweden, which joined NATO in 2023 and 2024, respectively. 97 Council of the EU, ‘EU defence cooperation: Council welcomes Denmark into PESCO and launches the 5th wave of new PESCO projects’ (Press Release, 23 May 2023), <https://www.consilium.europa.eu/en/press/press-releases/2023/05/23/eu-defence-cooperation-council-w elcomes-denmark-into-pesco-and-launches-the-5th-wave-of-new-pesco-projects/> accessed 4 October 2024. 96 Protocol on the concerns of the Irish people on the Treaty of Lisbon [2013] OJ L60/132 Article 3. 95 Article lJ.4(4)(n3). 94 An in-depth analysis and discussion of collective defence in international law is outside the scope of this article. A brief overview is, however, essential to understand EU Member States’ collective defence obligations and how they relate to UN principles. 93 Blake and Mangiameli (n16) 1228. 92 Martin (n20) 418-419; Sari (n 21) 438. The German Federal Court, however, clearly affirmed that the EU’s collective defence clause does not go beyond NATO’s collective defence clause. See German Federal Constitutional Court, Judgment on the Treaty of Lisbon (30 June 2009) para 386 <https://www.bundesverfassungsgericht.de/SharedDocs/Entscheidungen/EN/2009/06/es20090630_2bve 000208en.html> accessed 20 January 2025. 91 Fazio, ‘Collective defence in NATO’ (n 18) 8-9. These ‘special status’ countries are not required to disregard their positions to comply with mutual defence obligations. According to Sari, only these Member States are entitled to decline to provide military assistance when the gravity of the situation would call for a military response.98 However, Article 42(7) TEU does not clearly state which countries are covered by this clause and, this is something that cannot be determined without looking at thedrafting history of the article.99 According to some scholars, the clause could potentially apply also to Member States like Germany, where parliamentary authorisation of the use of force is constitutionally required.100 As Martin suggested, if a Member States’ parliament refuses to authorise the use of military force such a legal obstacle would exclude the State’s participation in military operations without it being considered in breach of the obligation to provide aid and assistance under Article 42(7) TEU.101 This confirms that the obligations arising under Article 42(7) TEU may be better understood as obligations of result rather than of means. In the case of an obligation of result, a state is generally presumed to be in breach if the envisaged outcome is not achieved, unless it can invoke a lawful excuse. By contrast, an obligation of means requires that a state undertakes appropriate and reasonable efforts, irrespective of whether the intended outcome is ultimately attained. The EU’s collective defence clause seemingly suggests that various degrees of commitment were envisioned for each member state based on the unique nature of their respective security and defence policies. Yet, this would translate in an evident asymmetry in military obligations, undermining the core purpose of the mutual defence clause, which is to ensure an equal sense of security among all parties involved.102 The fact that Ireland – and initially Germany, which now also provides lethal assistance – have, through the EPF, provided non-lethal military support to Ukraine, which is not an EU Member State but a candidate country, in the context of Russia’s war of aggression, suggests that this category of Member States would not be completely exonerated from the legal obligation to provide aid and assistance in the event of an invocation of Article 42(7) TEU; rather, they would be entitled to choose means of assistance which are not incompatible with their status or domestic law requirements.103 This contrasts with the argument that Member States are called ‘to examine on a case-by-case basis whether their status requires non-participation’ with the conclusion varying depending on the country.104 104 Blake and Mangiameli (n16) 1229; see also Dyson & Konstadinides (n71) 69. 103 House of the Oireachtas, ‘Ukraine War Dáil Éireann Debate’ (8 May 2024) <https://www.oireachtas.ie/en/debates/question/2024-05-08/74/> accessed 20 September 2024; German Federal Government, ‘The arms and military equipment Germany is sending to Ukraine’ (19 August 2024) <https://www.bundesregierung.de/breg-en/news/military-support-ukraine-2054992> accessed 20 September 2024; see also Cirlig (n45) 4; Martin (n20) 416. 102 Reichard (n24) 211; Blake and Mangiameli (n 16) 1228-1229. 101 Martin (n 20) 419. 100 Cirlig (n45) 4; Perot, ‘The art of commitments’ (n29) 52; Martin (n20) 419. The UK as well, at the time. As reported by Mills, ‘The Government ha[d] stated its intention to seek the approval of the House before committing military forces to action against ISIS in Syria. However, France’s invocation of a treaty obligation ha[d] raised questions among many observers as to whether a treaty obligation represents a critical national interest and, therefore, whether prior parliamentary approval would now need to be sought for expanding UK military operations against ISIS’. See Mills (n87) 4-5. 99 Reichard (n24) 211; Martin (n20) 419. 98 Sari (n21) 435. However, it should be noted that the CJEU has, in principle, no jurisdiction on CFSP and CSDP, and, therefore, Article 42(7) TEU.105 The CJEU only has jurisdiction over Article222 TFEU.106 Therefore, as with NATO, if any Member State, whether or not it falls within the aforementioned category, decides to provide little or no aid and assistance at all, there is no sanctioning mechanism to compel it to act otherwise.107 1.7 THE NATO CLAUSE The ‘NATO clause’, like the Irish clause, was not included in Article 5 MBT but was later incorporated into Article I-41(7) CT. Based on this clause, special caveats also apply to the23EU Members States that are members of NATO. This seems to imply that, for members of both organisations, mutual defence obligations arising from the NAT have primacy over those arising from the TEU.108 This is consistent with Article 8 NAT,109 as well as Article 30(2) VCLT.110 Therefore, the EU’s mutual defence obligation would only apply as long as it did not conflict with the prevailing obligation under the NAT.111 For this reason, before its invocation in 2015, it was thought that the EU’s mutual defence clause could only be triggered for attacks against non-NATO EU Member States.112 The French case has shown, however, that, in the event of an attack, members of both organisations can choose which of the two articles to invoke. It has also revealed that calling for one does not automatically trigger the other, though this does not preclude the possibility of simultaneously invoking both clauses if necessary.113 As highlighted by Fiott, ‘such a situation would raise chain of command, financing and transportation considerations’.114 The article could also potentially be invoked by a non-NATO EU Member State against a non-EU NATO Ally, unlike Article 5 MBT.115 In hypothesis, if attacked, Cyprus – or Greece which is in NATO, however – could, for example, activate the EU’s collective 115 The 2003 Berlin Plus framework agreement consists of classified letter exchanges between then-EU High representative Javier Solana and then-NATO Secretary General Lord Robertson. In one such letter, Solana allegedly stated that the ESDP and, therefore, also the EU’s mutual defence clause, would never be used against a NATO Ally. However, as Reichard noted, the Berlin Plus arrangements are not binding. Reichard (n24) 222. 114 Fiott, ‘Rising Risks’ (n113) 3. 113 Sari (n21) 425 and 435; Bakker et al (n19) 26; Daniel Fiott, ‘Rising Risks: Protecting Europe with the Strategic Compass’ (CSDS Policy Brief 10/2022, Centre for Security, Diplomacy and Strategy, 12 May 2022), 2 <https://csds.vub.be/publication/rising-risks-protecting-europe-with-the-strategic-compass/> accessed 20 September 2024. 112 Reichard (n24) 221. 111 As Sari has pointed out, this, however, is not the case for Article 222 TFEU. He argues that if a terrorist attack or a man-made disaster rises to the level of an armed attack or aggression, the solidarity clause could apply in parallel with the EU and NATO’s mutual defence clauses. In such cases, however, military assistance provided under Article 222 is not subject to the requirement that it be compatible with commitments undertaken within NATO. See Sari (n21) 439. 110 Vienna Convention on the Law of Treaties, 22 May 1969, 1155 UNTS 331, Article 30(2). 109 North Atlantic Treaty, 4 April 1949, 63 Stat. 2241, 34 UNTS 243, Article 8. 108 Blake and Mangiameli (n16) 1217. 107 Fazio, ‘Collective defence in NATO’ (n 18) 9. 106 Cirlig (n45) 7; Sari (n21) 425. 105 TEU (n2) Article 24(1); and TFEU (n 47) Article 275; see also Panos Koutrakos, ‘Judicial Review in the EU’s Common Foreign and Security Policy’ (2018) 67(1) International and Comparative Law Quarterly 1. defence clause against Turkey.116 Asamatter of fact, in 2020 Greece and Turkey were on the verge of war in the Eastern Mediterranean and, at one point, the Greek government made express reference to Article42(7) TEU.117 In such a scenario, members of both organisations could be subject to competing requests for assistance as they have only one set forces. Therefore, NATO obligations would probably take precedence over European obligations.118 Still, whether this precedence would truly apply also depends on the circumstances of the clause’s invocation.119 Additionally, this primacy of NATO over EU commitments does not amount to a ‘right of first refusal’ in favour of NATO. Despite the fact that the 2003 Berlin Plus arrangements did include a right of first refusal for NATO, even for peacekeeping operations, the launch of Operation Artemis in the Democratic Republic of Congo in June2003 made it very clear that this was not the case.120 The 1999 Helsinki European Council Conclusions had stated that the EU would act only in instances ‘where NATO as a whole is not engaged’,121 but as pointed out by Blake & Mangiameli, ‘this principle is a matter of policy and not of law and in no way means that the EU may only act when NATO has refused to implement a special operation’.122 The two organisations have, in fact, conducted parallel operations in the same geographical areas, such as in Kosovo, Afghanistan and theHorn of Africa. Finally, Reichard noted that, were a non-NATO EU Member State to be attacked, it could benefit from NATO’s mutual security guarantee ‘through the back door’.123 Indeed, were Ireland to be attacked, for example, it is hard to imagine that the US and the UK would refrain from intervening or impose missile restrictions; or at least it was hard to imagine before Trump returned to the White House. 2 STRATEGIC ANALYSIS ‘Mutual assistance clauses serve a dual purpose. They commit their signatories to stand up to a common threat and are thereby meant to deter potential aggressors. Their dual purpose places them at the crossroads between war and peace and the intersection between 123 Reichard (n24) 222. 122 Ibid; Blake and Mangiameli (n16) 1217. 121 European Council, Presidency Conclusions, Helsinki, 10-11 December 1999, para 27. 120 Daniel Keohane, ‘ESD and NATO’ in Giovanni Grevi et al (eds), European Security and Defence Policy: The First 10 Years (1999-2009) (European Union Institute for Security Studies 2009) 131; Reichard (n24) 130. 119 Fazio, ‘What happens if Trump invades Greenland?’ (n 50). 118 Perot, ‘The art of commitments’ (n29) 52. 117 Deen et al (n29) 41-42; see also Elie Perot, ‘Solidarity and Deterrence in the Eastern Mediterranean: An Analysis of the Delicate Question of Collective Defence Between EU Member States Vis-à-Vis Turkey’ (13/2021 Fondation pour la recherche stratégique (FRS), June 2021), 11-12 <https://www.frstrategie.org/sites/default/files/documents/publications/recherches-et-documents/2021/1 32021.pdf> accessed 16 June 2025. 116 Since Cyprus joined the EU in 2004, formal cooperation between the two institutions has stalled due to the unresolved dispute between Turkey, a non-EU NATO Ally, and Cyprus, a non-NATO EU Member State, over the latter’s sovereignty. Twenty years later, seemingly insurmountable obstacles still stand in the way of a peace deal and the two countries keep using their respective leverage, Turkey within NATO and Cyprus within the EU, to prevent formal meetings between the two institutions, blocking formal cooperation. For more information, see, e.g., Simon J Smith and Carmen Gebhard, ‘EU–NATO relations: running on the fumes of informed deconfliction’ (2017) 26(3) European Security 303. law and strategy’.124 With this dual role in mind, this Section analyses the 2016 EUGS and the2022Strategic Compass, as well as their related implementation strategies and progress reports. The strategic analysis reveals that, despite the EU’s growing role in defence, the Union places greater emphasis on unconventional threats – such as terrorism, cyber, hybrid, and space-based threats – than on traditional threats, which Article 42(7) TEU, like Article5NAT, was originally designed to address. The fact that this strategic focus has remained largely unchanged, even in the face of Russia’s war of aggression against Ukraine, suggests that the primacy of NATO’s mutual defence obligations over those of the EU is grounded not only in legal hierarchy but also in the EU’s limited capacity and mandate in the area of collective defence. While recent EU initiatives reflect growing ambition, they have yet to signal a fundamental rebalancing toward territorial defence. 2.1 THE 2016 GLOBAL STRATEGY FOR THE EUROPEAN UNION’S FOREIGN AND SECURITY POLICY – SHARED VISION, COMMON ACTION: A STRONGER EUROPE As the title suggests, the EUGS, which covered not only security and defence but all aspects of EU external action, aimed to initiate a new phase of European integration via common action, rather than merely developing a single strategic vision like the previous 2003European Security Strategy (ESS).125 Unveiled by then-HR/VP Federica Mogherini on 28 June 2016, the EUGS was adopted at a time when Europe was grappling with both internal and external challenges, including Britain’s decision to leave the EU, ISIS-driven terrorism,126 rising migration, and Russia’s revanchism, which had culminated in the illegal annexation of the Crimean Peninsula in March 2014, following its recognition of Abkhazia and South Ossetia’s independence in August 2008. As a consequence of this new strategic landscape, the word ‘defence’ was mentioned 57 times in the EUGS – 50 more than in the ESS – with ‘strategic autonomy’ featuring for the first time in a European strategy document.127 ‘The European Union will promote peace and guarantee the security of its citizens and territory’, the Strategy claimed,128 seemingly suggesting that the EU was preparing to take on a more active role in collective defence. To this end, the EUGS called for a sectoral strategy, the Implementation Plan on Security and Defence (IPSD),129 which aimed to 129 Council of the EU, ‘Council conclusions on implementing the EU Global Strategy in the area of Security and Defence’ (14149/16, 14 November 2016) <https://www.consilium.europa.eu/media/22459/eugs-conclusions-st14149en16.pdf> accessed 13 May 128 EUGS (n4) para 1, 7; emphasis added. 127 The concept had been first mentioned in the European Council Conclusions on CSDP of December 2013 in relation to defence industry, fifteen years after the 1998 Franco-British Saint Malo declaration had called for the Union to develop ‘the capacity for autonomous action, backed up by credible military forces […] supported by a strong and competitive European defence industry and technology’. See House of Commons, ‘Declaration on European Defence, British-French Summit, St Malo, 3-4 December 1998’ (HC 39, 1998-99, UK) <https://publications.parliament.uk/pa/cm199899/cmselect/cmdfence/39/39w17.htm> accessed 13 May 2025. 126 Nash Jenkins, ‘A Timeline of Recent Terrorist Attacks in Europe’ (Time, 20 December 2016) <https://time.com/4607481/europe-terrorism-timeline-berlin-paris-nice-brussels/> accessed 15 August 2025. 125 Nathalie Tocci, ‘The making of the EU Global Strategy’ (2016) 37(3) Contemporary Security Policy 461, 462. 124 Sari (n 21) 406. transform the EU into a more autonomous security and defence actor, particularly in the wake of Donald Trump’s first election victory as US President on 8 November 2016.130 This was followed by the adoption of the European Defence Action Plan (EDAP),131 comprising measures, such as the European Defence Fund (EDF), discussed later in this Section, which were designed to help EU Member States boost defence research and invest more efficiently on joint defence capabilities. The 2016 EUGS made express reference to the mutual assistance clause, which had been invoked for the first time only 7 months earlier, in the aftermath of the Paris attacks, for all the reasons and with the implications discussed in detail in the previous sections. ‘Mutual assistance’ is mentioned no less than 6 times in the document. Among the key priorities of the EU external action, it is stated that ‘Member States must translate their commitments to mutual assistance and solidarity enshrined in the Treaties into action. The EU will step up its contribution to Europe’s collective security, working closely with its partners, beginning with NATO.132 […] While NATO exists to defend its members – most of which are European – from external attack, […] Europeans must be better equipped, trained and organised to contribute decisively to such collective efforts, as well as to act autonomously if and when necessary […]’.133 Specifically, the Strategy called for deepening the partnership with NATO ‘through coordinated defence capability development, parallel and synchronised exercises, and mutually reinforcing actions to build the capacities of our partners, counter hybrid and cyber threats, and promote maritime security’.134 A month after the Strategy’s release, the EU and NATO adopted their first joint declaration, with the purpose of strengthening cooperation in 7 key areas, including hybrid threats, maritime operations, cybersecurity, defence capability development, partner capacity building, defence industry collaboration and joint 134 Ibid 37, emphasis added. 133 Ibid 20. 132 EUGS (n4) 9. 131 European Commission, ‘European Defence Action Plan: Towards a European Defence Fund’ (Press Release, 30 November 2016) <https://ec.europa.eu/commission/presscorner/detail/en/ip_16_4088> accessed 18 February 2025. 130 As pointed out by Sus, ‘the unique interinstitutional position of the HR gave Mogherini the advantage in combining the various ideas floating in the policy stream and framing them all as linked to the EUGS’s implementation, and thereby achieving wide-ranging policy change’. See, Monika Sus, ‘Supranational entrepreneurs: the High Representative and the EU global strategy’ (2021) 97(3) International Affairs 823, 840. 2025; see also Council of the EU, ‘Implementation Plan on Security and Defence’ (14392/16, 14 November 2016) <https://www.consilium.europa.eu/media/22460/eugs-implementation-plan-st14392en16.pdf> accessed 18 February 2025. exercises.135 On 6 December 2016, the Council136 and the NAC,137 endorsed 42 related proposals. The following year, 32 additional proposals were approved expanding cooperation into these as well as new areas such as counterterrorism, women, peace and security, and military mobility.138 In 2018, a second joint declaration139 introduced another area: resilience to chemical, biological, radiological and nuclear-related (CBRN) risks. Additionally, the Strategy stated that ‘[i]ncreased investment in and solidarity on counter-terrorism are key’ and that ‘the EU [would] support the swift recovery of Members States in the event of attacks through enhanced efforts on security of supply, the protection of critical infrastructure, and strengthening the voluntary framework for cyber crisis management’.140 The 2016 EUGS was followed by three implementation strategies in 2017, 2018 and 2019. The 2017 Implementation Strategy outlined key initiatives intended to advance the EU’s role as a security and defence actor. It noted that a Coordinated Annual Review on Defence (CARD) – designed to synchronise Member States’ defence planning – had been agreed by the Council, with a first full trial run scheduled for autumn 2017.141 The Strategy also reported that the Council had resolved to examine the activation of Permanent Structured Cooperation (PESCO), a concept introduced by the 2007 LT,142 which, according to the Strategy, had ‘the potential to make the definitive leap forward in European security and defence’.143 In addition, it highlighted the establishment of the EDF aimed at incentivising Member States to adopt a more collaborative approach by supporting coordination and enhancement of national defence research spending. Together 143 EEAS, ‘Implementing the EU Global Strategy: Year 1’ (n140) 22 and 23. 142 TEU (n2) Article 42(6). 141 Ibid 22. 140 European External Action Service, ‘From Shared Vision to Common Action: Implementing the EU Global Strategy: Year 1’ (10 January 2017), 21, emphasis added <https://www.eeas.europa.eu/sites/default/files/eugs-report-full_brochure_year_1.pdf> accessed 20 September 2025. 139 Council of the EU, ‘Joint Declaration on EU-NATO Cooperation by the President of the European Council, the President of the European Commission, and the Secretary General of the North Atlantic Treaty Organization’ (10 July 2018) <https://www.consilium.europa.eu/media/36096/nato_eu_final_eng.pdf> accessed 18 February 2025. 138 Council of the EU, ‘Council conclusions on the Implementation of the Joint Declaration by the President of the European Council, the President of the European Commission and the Secretary General of the North Atlantic Treaty Organization’ (14802/17, 5 December 2017) <https://www.consilium.europa.eu/media/31947/st14802en17.pdf> accessed 18 February 2025; NATO, ‘Common set of new proposals on the implementation of the Joint Declaration signed by the President of the European Council, the President of the European Commission and the Secretary General of the North Atlantic Treaty Organization’ (Press Release (2017) 174, 5 December 2017) <https://www.nato.int/cps/fr/natohq/official_texts_149522.htm?selectedLocale=en> accessed 18 February 2025. 137 NATO, ‘Statement on the implementation of the Joint Declaration signed by the President of the European Council, the President of the European Commission, and the Secretary General of the North Atlantic Treaty Organization’ (Press Release (2016) 178, 6 December 2016) <https://www.nato.int/cps/en/natohq/official_texts_138829.htm> accessed 18 February 2025. 136 Council of the EU, ‘Council Conclusions on the Implementation of the Joint Declaration by the President of the European Council, the President of the European Commission and the Secretary General of the North Atlantic Treaty Organization’ (15283/16, 6 December 2016) <https://www.europarl.europa.eu/cmsdata/121581/ST_15283_2016_INIT_EN.pdf> accessed 18 February 2025. 135 European Parliament, ‘Joint Declaration by the President of the European Council, the President of the European Commission and the Secretary General of the North Atlantic Treaty Organization’ (n30). CARD, PESCO and the EDF were presented as mutually reinforcing instruments, with the European Defence Agency (EDA) identified as playing a key supporting role.144 The First Implementation Report also highlighted progress made on EU-NATO cooperation, described as a ‘qualitative leap forward’.145 In addition to the 42 set of proposals agreed in Warsaw, the 2017 Implementation Report referred to the establishment of a new European Centre for Countering Hybrid Threats in Helsinki and emphasised joint efforts undertaken by the two organisations in ensuring coherence between the NATO Defence Planning Process (NDPP) and the EU Capability Development Plan (CDP).146 The 2018 and 2019 Implementation Strategies also highlighted how the EU and NATO had successfully deepened their partnership in the framework of the two joint declarations of 2016 and 2018, especially on military mobility, counterterrorism, cyber and maritime security.147 Despite the adoption of new security and defence initiatives, however, none of these documents referred to the mutual defence or the solidarity clauses. The Council Conclusions of June 2019 called on ‘Member States to discuss the lessons identified following the first activation of Article 42.7 TEU’148 and reminded them of the importance of mutual assistance and solidarity. Yet, there is no indication that such discussions have taken place. 2.2 THE 2022 STRATEGIC COMPASS FOR SECURITY AND DEFENCE The product of a two-year reflection process conducted by former HR/VP Joseph Borrell in tandem with the European Commission and EU Member States,149 the Strategic Compass was adopted by the Foreign Affairs and Defence Ministers of the 27 EU Member States on 21 March 2022, roughly a month after the war in Ukraine started, and endorsed by EU Heads of State and Government a few days later. Unlike previous EU security strategies, the Strategic Compass is characterised by a common threat analysis and a bottom-up approach.150 The word ‘defence’ is mentioned no fewer than 234 times in the strategy – including, for the first time ever, in the title – over 4 times more than in the EUGS, reflecting the heightened emphasis on defence as a consequence of war on the EU’s doorstep. In addition, mutual assistance is referred to 12 times in the Compass – twice as much than in the previous strategy. 150 EEAS, ‘A Strategic Compass for Security and Defence’ (n4) 7. 149 Council of the EU, ‘Council Conclusions on Security and Defense’ (8910/20, 17 June 2020) <https://www.consilium.europa.eu/media/44521/st08910-en20.pdf> accessed 24 February 2025. See also, Monika Sus, ‘Exploring the dynamics of policy change in EU security and defence: policy entrepreneurs behind the Strategic Compass’ (2023) 47(4) West European Politics 942, 948, 951, 952, 953, 954 and 956. 148 Council of the EU, ‘Council Conclusions on Security and Defence in the context of the EU Global Strategy’ (10048/19, 17 June 2019) <https://www.consilium.europa.eu/media/39786/st10048-en19.pdf> accessed 24 February 2025. 147 European External Action Service, ‘Implementing the EU Global Strategy: Year 2’ (25 June 2018), 8 <https://www.eeas.europa.eu/sites/default/files/eugs_annual_report_year_2.pdf> accessed 24 February 2025; European External Action Service, ‘The European Union’s Global Strategy Three Years On, Looking Forward’ (13 June 2019), 11 <https://www.eeas.europa.eu/sites/default/files/eu_global_strategy_2019.pdf> accessed 24 February 2025. 146 EEAS, ‘Implementing the EU Global Strategy: Year 1’ (n140) 24. 145 Ibid 24. 144 Ibid 23. In order to be able to act more rapidly and assertively, EU Member States have agreed in the Compass to develop an RDC of up to 5,000 troops by 2025. The RDC will replace the EU Battlegroups, multinational rapid reaction forces created for crisis management operations outside the EU which had become operational in 2007 but were never deployed. For the first time, the EU also stated its intention to conduct regular live exercises to increase defence interoperability and readiness. "We will continue to invest in our mutual assistance under Article 42(7) of the Treaty on European Union as well as solidarity under Article 222 of the Treaty on the Functioning of the European Union, in particular through frequent exercises", the Compass states.151 However, as with the previous strategy, the focus seems to remain on non-traditional threats. As Fiott has pointed out,152 these regular exercises seem, in fact, to be mostly aimed at responding to non-traditional attacks such as cyber attacks,153 hybrid attacks154 and even space-based attacks.155 Indeed, as Blockmans et al also noted, there is a strong focus on hybrid threats and tactics (the term hybrid appears 46 times) in the Compass, which ‘seems out of sync with the fact that Russia is waging a highly conventional war against Ukraine […]’.156 A strong emphasis is placed on the development of the EU Hybrid Toolbox, the Cyber Resilience Act, and further development of the Cyber Diplomacy Toolbox, the Foreign Information Manipulation and Interference (FIMI) Toolbox and adoption of the EU Space Strategy for security and defence. There is no mention in the Compass of how the EU intends to prepare for the eventuality of a traditional attack on its soil amid Russia’s aggression of Ukraine. TheCompass merely states that the EUMS could play a role in ‘the coordination of logistical support and assistance to Member States and third countries in a crisis, as well as the implementation of EU instruments such as the European Peace Facility or, upon Member States’ request, the mutual assistance clause, in line with the Treaty on European Union’.157 This is because most EU Member States are also members of NATO and consider its mutual defence guarantee, enshrined in Article 5 NAT, the cornerstone of their security. However, following the outcome of the 2024 US Presidential election, which saw Donald Trump elected for a second non-consecutive term, this reliance faces new strategic uncertainty.158 With the potential to unlock €800 billion for defence, the ReArm Europe Plan/Readiness 2030 – unveiled by the European Commission two months after Trump’s return to the White House – is a clear attempt to develop autonomous defence capabilities 158 Fazio, ‘Collective defence in NATO’ (n 18) 8-9. See also Emma Ashford and MacKenna Rawlins ‘American Roulette: Scenarios for US Retrenchment and the Future of European Defense’ (Policy Paper, Stimson Center, 8 July 2024) <https://www.stimson.org/2024/american-roulette-scenarios-for-us-retrenchment-and-the-future-of-europe an-defense/> accessed 20 September 2024. 157 EEAS, ‘A Strategic Compass for Security and Defence’ (n4) 38. 156 Steven Blockmans et al, ‘The EU’s Strategic Compass – A guide to reverse strategic shrinkage?’ (CEPS Policy Insights 2022, Centre for European Policy Analysis, 14 March 2022), 8 <https://cdn.ceps.eu/wp-content/uploads/2022/03/CEPS-PI2022-14_EU-Strategic-Compass.pdf> accessed 24 February 2024. 155 Ibid 34 and 36. 154 Ibid 34 and 39. 153 EEAS, ‘A Strategic Compass for Security and Defence’ (n4) 35 and 39. 152 Fiott, ‘Rising Risks’ (n113). 151 Ibid 28. France played a leading role in pushing for this. See, e.g., Sus, ‘Exploring the dynamics of policy change in EU security and defence’ (n149) 954. and reduce dependency from the US. The recent agreement between France and the UK to deepen bilateral cooperation on nuclear deterrence159 can also be seen as a direct response to the growing uncertainty surrounding the US nuclear umbrella, despite reassurances made at the NATO Hague Summit.160 As in the previous Strategy, considerable attention is given to the EU-NATO relationship. The Executive Summary states that ‘A stronger and more capable EU in the field of security and defence will contribute positively to global and transatlantic security and is complementary to NATO, which remains the foundation of collective defence for its members’. The partnership with NATO is the first topic addressed in the ‘Partner’ section – one of four pillars of the Compass, alongside Act, Secure, and Invest. ‘The EU’s strategic partnership with NATO is essential for our Euro-Atlantic security’, the Compass affirms.161 The document claims that cooperation with NATO will be further strengthened in the areas covered by the 2016 and 2018 Joint Declarations.162 The real game changer, according to the Compass, however, will be ‘moving to joint and inclusive exercises’, which will allow the two organisations to build trust, increase interoperability and deepen cooperation.163 In 2022, under the Plan for Implementation of Parallel and Coordinated Exercises (PACE) 2022-2023, NATO staff joined the planning and conduct phases of the EU Integrated Resolve (IR) 22 exercise, focusing on the management of hybrid crises with internal and external dimensions.164 The following March, staff from the European Commission, the General Secretariat of the European Council, the Council, and the EEAS participated in the planning and conduct of NATO’s crisis management exercise (CMX) 2023, also focusing on a hybrid crisis scenario.165 Finally, the Strategic Compass stresses the need to invest more and better in defence capabilities and cutting-edge technologies. The Strategic Compass was followed by two Progress Reports in 2023 and 2024. In relation to the mutual defence clause specifically, the 2023 Progress Report stated that ‘[t]o further strengthen our mutual assistance in case of an armed aggression, we have conducted exercises on Article 42(7) TEU in scenarios involving cyber, hybrid and space-related threats, and will continue to do so on a regular basis’.166 This claim was reiterated in the 166 European External Action Service, ‘Annual Progress Report on the Implementation of the Strategic Compass for Security and Defence’ (20 March 2023) 9, emphasis added <https://www.eeas.europa.eu/sites/default/files/documents/2023/StrategicCompass_1stYear_Report.pdf> accessed 26 April 2025. 165 For more information, see <https://www.nato.int/cps/en/natohq/news_212527.htm> accessed 26 April 2024. 164 For more information, see <https://www.eeas.europa.eu/eeas/eu-integrated-resolve-2022-eu-ir22-parallel-and-coordinated-exercisespac e_en> accessed 26 April 2024. 163 Ibid 54. 162 Ibid. 161 EEAS, ‘A Strategic Compass for Security and Defence’ (n4) 53, emphasis added. 160 Federica Fazio, ‘A Dissenting Opinion on The Hague Summit: the Real Winner is NATO, Not Trump’ (DCU Brexit Institute, 30 June 2025) <https://www.dcu.ie/blog/2151/dissenting-opinion-hague-summit-real-winner-nato-not-trump> accessed 8 July 2025. 159 UK Prime Minister’s Office and The Rt Hon Sir Keir Starmer KCB KC MP, ‘Northwood Declaration: 10 July 2025 (UK-France joint nuclear statement)’ (Press Release, 10 July 2025) <https://www.gov.uk/government/news/northwood-declaration-10-july-2025-uk-france-joint-nuclear-state ment> accessed 12 July 2025. 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