Nobel Peace Laureate René Cassin played a key role in the creation of UNESCO; one that highlights its conception and central mission as an organization to pursue human disarmament, and with it to eliminate the civil-military distinction by turning everyone into a civilian. This study examines the “moral disarmament” movement which arose after the First World War, the idea that it was important not just to eliminate physical weapons but change the way people thought about war by having them embrace and understand each other and their common humanity. It pays close attention to the role that history played in this process, particularly the fierce debate over the origins of the First World War. Cassin was an important member of this movement, and his career helps trace its evolution, from the League of Nations to the World Disarmament Conference, and finally to the Second World War and the Conference of Allied Ministers of Education which lead to the creation of UNESCO in 1945.