The European Union’s nascent role in the field of collective defense: between deliberate and emergent strategy

Over the past 15 years, the EU has gradually become more involved, de jure and de facto, in the field of collective defense. This underappreciated evolution occurred in three phases: first, an initial phase, from the steps leading up to the Lisbon Treaty, which incorporated collective defense into the EU’s mandate via Article 42.7 TEU, to the first activation of this provision following the November 2015 Paris attacks; second, a phase of indirect development, with the launch of policies on military mobility and hybrid threats, tangentially linked to collective defense; and third, a phase of direct yet incomplete affirmation, with calls to operationalize Article 42.7 TEU and the signaling of the EU as a collective defense framework during crises with Turkey and Russia. The EU’s modest forays in collective defense, while resulting from both a deliberate and emergent strategy, have become more conscious over time and thus increasingly difficult to ignore.