The main objective of this paper is to present the transition from military conflict to the development of peace and security in the Western Balkans, mainly through the engagement of external actors. Although the paper addresses the role of NATO and OSCE, the emphasis is on a comparative analysis of UN and EU conflict prevention and resolution and peacebuilding as deployed in two distinct phases: first, the war and immediate post-war period (1991–1999), characterised by the UN’s dominant role and involvement; and second, the period after 2000, marked by the start of the democratic transition in the Western Balkans and the EU’s rise as a major external actor. The paper argues that during the first phase, external influence through the agency of several UN peacekeeping operations together with EC as well as joint UN-EC initiatives aimed to create the conditions for the absence of direct violence – negative peace. On the other hand, the second phase was and currently remains characterised by the use of predominantly EU instruments that seek to build positive peace via cooperation using several programmes designed specifically for this post-conflict region – especially the policy of conditionality and CSDP operations. The paper aims to detect and analyse the activities of the UN and EC/EU in these two distinct phases, determine their character and influence on conflict prevention, conflict resolution and peacebuilding in the region, relying on the “hourglass model” for resolving conflict.