Résumé : The European Union today faces a heated, tantalising debate. Since the early years of the integration process, European defence has caused irreducible complications because defence, and thus the security of one’s borders, citizens, interests and values, is an inherent characteristic of the sovereignty of the Westphalian State. If at the time of the European Communities’ creation, conferring part of one’s sovereignty to a supranational entity might have appeared as the natural course of events after prior integration had been achieved in the low-politics economic sphere, over time the debate has become more and more controversial. So far, we have witnessed a non-linear process of building a Europe de la défense, made of rapid historical accelerations, fuelling greater cooperation, followed by gradual slowdowns. Still, by drawing a common thread between these waves of integration, we can see how periods of crisis have largely been influential in spurring today’s EU Member States to agree on a commonality of purpose, an overall strategic vision, and a concrete direction to guide future steps to be taken. Here, some may argue that these joint efforts, if taking place subsequently to an external impetus such as a looming threat burdening the Continent, may be neither wanted nor sought-after, but are just the result of a historical necessity. Yet, the de-sire to seek or be able to provide greater security is by definition dictated by the perception of an external threat undermining what describes and defines us.Today, for the first time since WWII, multi-dimensional warfare has returned to the Old Continent in the wake of Russia’s aggression against Ukraine. Hence, the global security environment appears highly damaged and increasingly deteriorating, giving rise to more uncertainty and more need for cooperation in achieving newfound stability. All the same, the EU27 have been caught practically unprepared to respond to this event, giving evidence of the great strategic dependence they have on the transatlantic allies. While this harsh reality has jolted all EU Member States into greater cooperation, investment, and coordination in the defence field, only a few countries might be willing to channel these efforts to pursue a common strategic foresight towards European Strategic Autonomy in Defence. Yet, what is rather paradoxical about this debate is that the same EU countries that would most benefit from a European defence system, being directly exposed to incumbent threats – such as the eastern flank ones – are those least in favour of engaging in further cooperation in EU defence. The more Europeans feel weak and dependent on Washington, the more they shy away from any efforts that might annoy the Pentagon, thus relegating their protection to others under the NATO umbrella. In this regard, we might reckon that similar postures, much like the highly diffuse European tendency to free-ride, are not only a counter-productive and sub-optimal option but also a self-perpetuating cycle that is bereft of profit margins.Although the French historical approach towards European defence has not been devoid of controversy, France has always harboured characteristic ambitions towards a Europe de la défense. In particular, its contribution to greater cooperation in the defence domain has never shied away from encouraging the quest for European Strategic Autonomy by both highlighting the strategic dependencies on which the Union hangs and leading the way to remedying EU defence deficiencies. These dependencies, both economic and decisional, are in fact symptoms of internal weaknesses in European defence and, more broadly, of the EU. To this end, for the Union to gain more credibility in the international system, face present-day increased geopolitical challenges, and merit the status of Global Defence Actor, it must take its fate into its own hands and, in small doses, take higher responsibility to convey more assertiveness. Still, as a mutually beneficial solution, greater strategic autonomy of the EU27 would not only overcome European defence fragmentation but also allow for a recalibration of the Allies’ contribution within NATO to better fix the Alliance’s gaps and strengthen transatlantic ties. If considering today’s major geopolitical threats and systemic rivalries, achieving such an objective will soon no longer be optional or preferable, but imperative instead. As such, a multi-speed Europe de la défense that builds on the aspirations of a “capable and willing” few to gradually expand in scope and ambition turns out to be the most logical choice. After decades of compromises and scarce results, the French potential to set such a project in motion may thus prove to be the winning strategy. Notably, the research question around which the present thesis revolves is the following:How and why might France constitute the best-suited country to promote multi-speed European defence integration, allowing the Union to become a strategically autonomous Global Defence Actor?