As a theoretician, Aron was, like Clausewitz, keen to understand the nature of war. He was also an attentive witness to the ways in which war changed. While his thought is not as systematic as the Prussian thinker’s, it nevertheless sheds light on the contemporary strategic context in three ways. First, his approach to international relations leads to the definition of the current system as multipolar and heterogeneous. Second, his typology of war reveals that interstate war has, since 1945, all but been replaced by nuclear deterrence and guerilla warfare. Finally, his analysis of the relationship between democracy and war brings to light a tension between the principles of liberty that define western democracy domestically and the hegemonic character of their military interventions on the international scene.