In a corpus as capacious as Raymond Aron's, many books might qualify as his chef-d"oeuvre. For example, Introduction to the Philosophy of History could be considered his most foundational work in that the character and limits of historical intelligibility are first discussed here, and this theme would animate nearly all of Aron's postwar writings. The Century of Total War, by contrast, is a masterful historical account of the military, economic, and political revolutions of the twentieth century that reads as true and insightful today as it did when it was first published. In Clausewitz: Philosopher of War, Aron produces perhaps his most academic or scholarly book, rediscovering and reengaging in the old debates surrounding this central thinker. And finally, The Opium of the Intellectuals is a delicious (albeit trenchant) polemic where Aron repeatedly punctures such sacrosanct ideas as the "Left," "Revolution," and the "Proletariat."¹ But however impressive each of these works is, Peace and War surely deserves to be mentioned alongside them as one of Aron's finest intellectual achievements—and this in many ways because it combines all of the aforementioned elements into a systematic whole. Foundationally, Peace and War enabled Aron to concretize his long meditations on the character or nature of international politics; historically, he presents a lucid analysis of the postwar international system in order to pinpoint its unique attributes; academically, he enters into a range of debates with philosophers and scholars both past and present, from Montesquieu to Morgenthau; and finally, polemically, he deflates the pretensions of behaviorists, positivists, and others who continue to argue and to hope that international relations can be developed into a rigorous science akin to economics.²