The main aim of this thesis is to introduce a new way of thinking about security within International Relations by developing a model that can be used to explain the relationship between terrorism and organised crime. Referred to as the crime-terror continuum (CTC), the model identifies six major points of convergence between the terrorist and criminal worlds. The crime-terror continuum seeks to move away from the traditional confines of International Relations as encapsulated within realist thought. After providing an overview of the limitations of traditional theories, and a working definition of terrorism and organised crime, this thesis applies an alternative conceptual framework - based on a combination of applicable assumptions about security presented by the Copenhagen School, Ken Booth and Mohammed Ayoob - to an understanding of the threats posed by terrorism and organised crime. It also incorporates the understanding of the contemporary security environment provided by the globalisation and netwar proto-paradigms as a way to go beyond debates about concepts by seeking to understand the operational and organisational dynamics of contemporary security threats. Paying special attention to the argument that non-state actors can be equal to state actors in the security domain, this thesis highlights that competition over state functions and territory continues to play an integral role. The alternative view of security and the CTC are subsequently applied to two case studies: Russian Organised Crime and the Revolutionary Armed Forces of Colombia. Despite illustrating different aspects of the CTC, these case studies highlight the ability of the conceptual framework and the CTC to explain and understand the post-Cold War security environment.

L’objectif de la présente recherche portant sur l’évolution du droit des États à recourir à la force dans les relations nternationales est de montrer suivant une approche historique fondée sur le droit international que la pratique des États en la matière a changé. Effectivement, du droit de « faire la guerre » reconnu comme un droit souverain, passant par les premières tentatives de son encadrement au XIXe siècle, la rupture significative est venue en 1945 avec la création de l’ONU ; la Charte des Nations Unies ayant consacré un principe d’interdiction du recours à la force, exception faite de la légitime défense et de l’autorisation du Conseil de sécurité. Toutefois, aucune précision n’ayant été apportée sur la forme que doit prendre cette autorisation du Conseil de sécurité, dès 1966 comme dans l’affaire rhodésienne, ce dernier autorisait explicitement l’usage de « la force ». À partir de 1990, il prend de l’assurance avec la technique de l’autorisation et retient la formulation implicite d’« autorise les États Membres à user de tous les moyens nécessaires ». Cependant, il arrive qu’une résolution du Conseil ne soit ni n’explicite, ni implicite, mais des États interviennent, arguant de l’existence d’une autorisation implicite du fait de l’émergence des doctrines comme « guerre préventive », « guerre contre le terrorisme » ou encore « intervention humanitaire ». Des cas d’interventions menées en 1992 au Libéria, 1999 en Sierra Leone et au Kosovo et en 2003 contre l’Irak, sont illustrateurs. Ainsi, sur la base de l’interprétation des résolutions du Conseil, l’autorisation implicite tend à devenir la règle en matière de maintien de la paix et de la sécurité internationales. Dès lors, afin d’éviter de réduire le jus ad bellum à un unilatéralisme excessif, et en démontrant la conformité de l’autorisation implicite au régime juridique établi du recours à la force en droit international, nous invitons à la redéfinition de celle-ci. / The purpose of this research on the evolution of the right of States to use force in international relations is to show, following a historical approach based on international law, that State practice in this area has changed. Indeed, from the right to "make war" recognized as a sovereign right, passing through the first attempts of its leadership in the nineteenth century, the significant rupture came in 1945 with the creation of the UN; the United Nations Charter has enshrined the principle of the prohibition of the use of force,except for the self-defense and the authorization of the Security Council. However, since no details were given as to the form this authorization of the Security Council should take, as early as 1966, as in the Rhodesian case, the latter explicitly authorized the use of "force". From 1990, he gained confidence with the technique of authorization and retained the implicit formulation of "authorizes Member States to use all necessary means". Though, sometimes a resolution is neither explicit nor implicit, but states intervene,arguing the existence of an implied authorization because of the emergence of theories like"preventive war","war on terror" or "humanitarian intervention". Cases of interventions in 1992 in Liberia, 1999 in SierraLeone and Kosovo and in 2003 against Iraq are illustrators. So, based on the interpretation of Council resolutions, implied authorization tends to become the rule in the maintenance of international peace and security. Therefore, to avoid reducing the jus ad bellum to excessive unilateralism, and by demonstrating the conformity of the implied authorization with the established legal regime of the use of force in international law, we invite the redefinition of this one.