This dissertation is an interdisciplinary study on the external ‘Responsibility to Protect’ (R2P) and international law. It focuses on the legal customary process on jus ad bellum by which states try to address the gap between the legitimacy and legality of humanitarian intervention to protect human security within a state against genocide, war crimes and crimes against humanity. The development of specific legal rights for the Security Council, regional organisations and ‘coalitions of the willing’ to protect by military means is examined through case studies of humanitarian interventions after the Cold War. Constructivist perspectives on security and norms are contrasted with legal positivist analyses of customary law, the applicable law ...