For a decade, the EU and NATO have both claimed to have a relationship purported to be a Strategic Partnership. However, this relationship is widely understood by both academics and practitioners to be problematic. Although not denying that the relationship is problematic, it is claimed here that the argument, whereby the EU and NATO simply do not cooperate, is very limited in its value. In fact, it is argued that the two organisations cooperate far more, albeit less efficiently, outside of the formal Agreed Framework for cooperation. According to the formal rules of Berlin Plus/Agreed Framework (BP/AF), the EU and NATO should not cooperate at all outside of the Bosnia Herzegovina (ALTHEA) context. This is clearly not the case. The fundamental aim of this thesis is to investigate how this cooperation - beyond the BP/AF has emerged. Above all, it asks, within a context where formal EU-NATO cooperation is ruled out, what type of cooperation is emerging? This thesis attempts to explain the creation and performance of the informal EU-NATO institutional relationship beyond Berlin Plus. This thesis, drawing on insights from historical institutionalist theory and by investigating EU-NATO cooperation in counter-piracy, Kosovo and Afghanistan, puts forward three general arguments. First, in order for informal EU-NATO cooperation to take place outside of the BP/AF, cooperation is driven spatially away from the central political tools of Brussels, towards the common operational areas and hierarchically downwards to the international staffs and, in particular, towards the operational personnel. Second, although the key assumptions of historical institutionalism (path dependency, punctuated equilibrium and critical junctures) help to explain the stasis of the EU-NATO relationship at the broad political and strategic level, a more complete understanding of the relationship is warranted. Including theoretical assumptions of incremental change helps to explain the informal cooperation that is now driving EU-NATO relations beyond Berlin Plus. Finally, this thesis makes the fundamental claim that the processes of incremental change through informal cooperation reinforce the current static formal political and strategic relationship. Events and operational necessity are driving incremental change far more than any theoretical debates about where the EU ends and NATO begins. Until events force a situation whereby both organisations must revisit the formal structures of cooperation, the static relationship will continue to exist, reinforced by sporadically releasing the political pressure valve expedited through the processes of informal cooperation. If the EU and NATO are to truly achieve a Strategic Partnership , it will stem from an existential security critical juncture and not from internal evolutionary processes.

Les Balkans occidentaux (BO), déchirés après 1989 par les guerres dont les plus sanglantes et les plus problématiques en Bosnie-Herzégovine, au Kosovo, et en Albanie, ne pouvaient plus laisser indifférentes les puissances occidentales, et en particulier l’OTAN et l’UE. La survenue de ces conflits a confronté en effet les pays européens à la guerre près de chez eux signifiant une éventuelle déstabilisation de la région et la gestion d’un grand nombre d’immigrés en provenance des BO. C’est pourquoi l’OTAN et l’UE se sont depuis largement investies dans des missions de pacification et de reconstruction étatique dans cette région, par la mise en place de politiques de sécurité et de défense, puis par le biais de politiques d’élargissement. L'action de ces différentes organisations, à côté de celle des BO, a permis la fin de la guerre et une certaine stabilisation de ces pays. Mais, cette dernière est loin d'être complétement acquise. En effet, c'est la non consolidation des institutions étatiques et de la démocratie qui menace encore l’effondrement de l’Etat et qui continue à constituer un enjeu de taille pour les pays des BO.Notre thèse a pour objet d’analyser l'évolution de la stabilisation des BO depuis la chute du mur de Berlin en étudiant et en mettant en confrontation des ensembles complexes de relations entre acteurs, enjeux, moyens et processus. Afin d'analyser ce processus complexe, nous proposons un modèle qui s'appuie sur le concept des « communautés de sécurité » (CS) de Deutsch et al. (1957). Cependant, pour les besoins de notre étude, nous reconceptualisons ce concept à l’aide de variables que nous avons choisies en européanisation et en démocratisation que les auteurs n’avaient pas pu prévoir à l’époque de la rédaction des CS.Ainsi, le concept de CS reconceptualisé permet de répondre à notre problématique: pourquoi et comment une CS comprenant les pays de la région encore instable des Balkans occidentaux se construit-elle sur le continent européen autour de l'OTAN et de l'UE, depuis la chute du Mur de Berlin ?Notre hypothèse est la suivante : la construction d’une CS s’explique par la combinaison de deux éléments : d’une part la pression exogène des organisations régionales exigeant des changements concrets en termes de démocratisation et de sécurisation, et d’autre part l’acceptation de ces exigences de la part aussi bien des élites que des populations des pays concernés. En d’autres termes, plus la pression des organisations régionales est perçue comme légitime et mise en œuvre, plus la création d’une CS est probable.La variable dépendante que nous analysons est la construction d’une CS européenne comprenant les Balkans occidentaux (CSEBO) pluraliste. Les moyens de construction de cette communauté de sécurité correspondent à nos variables indépendantes choisies en sécurité, européanisation et démocratisation et qui sont de deux types : endogènes et exogènes. Il s’agit d’une part, des variables portant sur le rôle des facteurs et acteurs externes (OTAN et UE) en vue de la stabilisation des BO, et donc de leur contribution à la construction de la CSEBO. Il s’agit d’autre part, d’une série de variables endogènes portant cette fois-ci sur le rôle des facteurs et acteurs internes (élites et populations des pays des BO) dans la formation de la CSEBO. Nous montrons que les niveaux interne et externe sont en permanente interaction.Les résultats de notre étude, obtenus dans le cadre de la méthode de process-tracing à partir de sources primaires et secondaires, ainsi que d’entretiens semi-directifs, montrent un découpage dans le temps dans la construction de la CSEBO: avant et après 2000. Ainsi une première période allant de la chute du Mur de Berlin jusqu'au début des années 2000 connaît l’absence quasi-totale des conditions constitutives des CS et donc la CSEBO est très embryonnaire ici. Nous montrons ensuite qu’une CSEBO se construit progressivement à partir du début des années 2000. / The Western Balkans (WB) were torn apart after 1989 due to wars, which were particularly cruel and problematic in Bosnia and Herzegovina, in Kosovo and in Albania. Western powers, and especially NATO and EU, could not anymore turn a blind eye. These conflicts indeed confronted European countries to war in a neighbouring state which could lead to destabilization of the region and to more migrants coming from the WB. This is the reason why NATO and UE have since been deeply involved in peace building and state building missions throughout the region. They started with implementing security and defense policies, then turned to enlargement policy. These organisations’ actions, as well as the efforts done by the WB, led to the end of the war and, to a certain extent, to a stabilization of these countries which is however not fully achieved. WB State security is indeed still a major objective. The threat lies nowadays in the non consolidaton of state institutions and democracy.Our thesis is aiming at analyzing the stabilization of the WB since the fall of the Berlin wall. It will focus on studying and confronting a complex set of actors, goals, means and processes in order to have a better understanding of the evolution of the stabilization of the region. In order to analyze this complex process, we are using a model based on the concept of « security communities » (SC) developed by Deutsch and al., at the end of the 1950’s. However, for the need of our study, we will « reconceptualize » this concept using several variables selected in europeanisation and democratisation studies which the authors could not have predicted at the time they elaborated their concept of « security communities ».Therefore, the concept of SC, « reconceptualised », helps answering our research problem : why and how has a SC including countries from the instable region of the Western Balkans been built on the European continent, around NATO and the EU, since the fall of the Berlin wall ?Our research hypothesis consists in the combination of two elements to explain the building of a SC: on one side, an exogenous pressure from regional organizations imposing concrete changes in terms of democracy and securitization and, on the other side, the acceptance of these demands from both the elites and the population of the concerned countries. In other terms, the more legitimized and implemented the pressure from these regional organizations is, the more probable is the creation of a SC.The dependent variable that we analyze is the building of a pluralistic European SC which includes the Western Balkans. The means for building this security community correlate with our independent variables which are endogenous and exogenous and have been selected in security, democratisation and europeanisation studies. On one side, exogenous variables stand on the role of external actors and factors (NATO and the EU) leading to the stabilization of the WB, and therefore to their contribution to the building of an European security community including the Western Balkans (ESCWB). On the other side, there is a range of endogenous variables being the role of internal actors and factors (elites and populations of the WB) in the shaping of ESCWB. We will show that both internal and external levels are in constant interaction.Our study results based on primary and secondary sources as well as semi-directed interviews and using the « process-tracing » method highlight two distinct periods regarding the building of the ESCWB: before and after the year 2000. Thereby between the fall of the Berlin wall and the year 2000, there is almost a complete lack of the necessary conditions to build a SC and therefore the ESCWB merely exists in an embryonic form. ESCWB then progressively emerges from the beginning of the 2000’s.