The course aims to define and elaborate on the concept of military security as it developed after the Second World War. The time span is determined by the ineluctable revolution that the discovery and use of nuclear weapons ushered both in terms of military doctrine and of power politics. Starting with a reflection on the reasons of the early failure of collective security, the course will first focus on the crucial hallmarks of security in a bipolar international system, making a clear distinction between States included in, and excluded from, a multilateral alliance. It will then take into consideration the major challenges posed to military security by newly emerging threats as the former was consolidating after the end of the Cold War.