The Treaty on European Union (Maastricht) was signed, creating the EU’s Common Foreign and Security Policy (CFSP) as a distinct cooperation pillar—an essential political foundation for later EU–NATO engagement on crisis management and defence coordination.
The Maastricht Treaty entered into force, formally establishing the European Union and operationalising CFSP structures that later interfaced with NATO’s crisis-management role and Euro-Atlantic security architecture.
The EU–NATO Declaration on the European Security and Defence Policy (ESDP) provided a formal political basis for cooperation in crisis management and conflict prevention, including principles such as consultation, transparency, and respect for each organisation’s decision-making autonomy.
The Berlin Plus arrangements were agreed, enabling the EU (under defined conditions) to access NATO planning and assets for EU-led operations where NATO as a whole is not engaged—establishing a practical mechanism for EU–NATO operational cooperation.
The EU launched Operation Concordia in (then) FYR Macedonia, taking over from NATO’s Operation Allied Harmony. It is widely cited as the EU’s first military operation and the first to use NATO assets under Berlin Plus—an early test of EU–NATO crisis-management cooperation.
The EU launched EUFOR ALTHEA in Bosnia and Herzegovina after NATO decided to hand over its peacekeeping mission, making ALTHEA a long-running and high-profile example of EU–NATO cooperation through Berlin Plus arrangements.
At the Wales Summit, NATO leaders underscored the value of a stronger European defence and called for further NATO–EU dialogue and cooperation, including on emerging challenges such as cyber and hybrid threats and on areas like maritime security and capacity building.
EU and NATO leaders signed the Warsaw Joint Declaration, committing to strengthen cooperation across priority areas (commonly cited as including countering hybrid threats, operational cooperation, cyber, defence capabilities, and coordinated exercises), and setting a new, more systematic framework for practical cooperation.
NATO launched Operation Sea Guardian in the Mediterranean, creating an operational platform that later supported and coordinated with EU maritime missions via information-sharing and de-confliction mechanisms, reinforcing day-to-day EU–NATO cooperation at sea.
The Council of the EU adopted conclusions on implementing the 2016 EU–NATO Joint Declaration, endorsing 40+ concrete proposals prepared by the EU High Representative/Vice President and the NATO Secretary General—turning Warsaw commitments into an implementation agenda.
A Memorandum of Understanding was signed in Helsinki to establish the European Centre of Excellence for Countering Hybrid Threats, with NATO and the EU participating in its activities—an institutional milestone supporting coordinated resilience against hybrid challenges.
NATO’s Secretary General publicly welcomed the launch of Permanent Structured Cooperation (PESCO) while stressing complementarity with NATO, reflecting a key EU–NATO theme: strengthening EU defence efforts in ways that reinforce transatlantic security.
EU member states (25) made PESCO legally binding, formalising a major EU defence cooperation framework that is frequently discussed alongside EU–NATO cooperation goals such as capability development and military mobility.
EU and NATO leaders signed the Brussels Joint Declaration, explicitly building on the Warsaw framework and updating priority areas for cooperation—reinforcing the practice of setting shared deliverables and reviewing progress jointly.
The Council approved the Strategic Compass, an action plan to strengthen EU security and defence by 2030; it frames partnerships (including with NATO) as a core pillar and situates EU capability and resilience efforts in the post-2022 security environment.
EU–NATO cooperation and security policy milestones (1991–2022)
