The canonical reading of Jaurès’s L’Armée nouvelle presents this work as an outdated reflection on the establishment of a socialist society supervised by intermediary bodies whose military training would be a major asset. Our reading goes beyond this historically situated approach to Jaurès’s book. We show that The New Army is not just a response to the General Staff, even less a ‘theorisation’ of the transition to socialism, but that its aim is to rehabilitate the founding principles of democratic institutions (ancient and modern), which rest on the constitution of an army of citizens: The ‘proletarian-soldier’ of Jaurès is none other than the ‘farmer-soldier’ of the ancient city and of Year 2 of the French Revolutionary calendar, transposed to the Industrial Age. Relying on a game-theoretical model, we highlight that this defence of democratic institutions is backed by a discourse of the economics of war prevention in terms of self-protection.