The book in question is Raymond Aron’s systematic treatise on international relations, commonly known in English as Peace and War: A Theory of International Relations. It is not a narrative history or a memoir but an analytical work that tries to define the field of international relations, explain the structure of interstate systems, and assess the ends and means of state action, especially war and peace.
Aron begins from the distinctive character of international relations: they are relations among political units—primarily states—that recognize no superior authority capable of settling their disputes and enforcing decisions. Domestic politics takes place within a hierarchy and under a more or less effective monopoly of legitimate violence; international politics takes place among sovereign units for which force remains a permanent possibility. This does not mean that international life is pure anarchy or that law and institutions are irrelevant. It means that the possibility of war shapes the calculations of statesmen and the meaning of diplomacy, alliances, security, and law.
Against narrower approaches, Aron insists that international relations cannot be reduced to economics, law, or ideology. He treats the field as “diplomatic-strategic” behavior: states must estimate their power, choose allies, manage threats, and decide when force is usable. Power is central, but Aron does not treat it as a simple quantity. Power is a relation, composed of military capacity, resources, geography, alliance commitments, legitimacy, and the perceptions of others. Military force is especially important because states ultimately rely on it, yet it is not the only currency of international politics.
The book develops a conceptual vocabulary for comparing international systems. Aron distinguishes the “international system” from “international society” and from transnational exchanges. The system is the ensemble of interactions among political units, especially those involving the risk of war. Within systems, he compares configurations of power—above all multipolar and bipolar arrangements—and examines the balance of power. He is skeptical of the idea that equilibrium is automatic. A balance may be produced by policy, by geography, by alliances, or by prudence; it is not a machine that runs by itself. The statesman’s judgment therefore matters.
Aron also distinguishes homogeneous from heterogeneous international systems. In a homogeneous system, the principal states share a similar conception of political legitimacy and internal order; in a heterogeneous system, they are divided by regime type, ideology, and conceptions of legitimacy. Heterogeneous systems tend to make conflicts more ideological and less easily limited, because the adversaries do not merely dispute territory or interest but question each other’s domestic order. This distinction is one of the book’s most influential analytical devices, though Aron uses it as a tool of historical comparison rather than as a rigid law.
The treatise draws extensively on history: the Greek city-states, the Italian Renaissance, the European state system, the revolutionary and Napoleonic wars, the two world wars, and the Cold War. These cases are not used as mere decoration. They allow Aron to compare how different systems generate different kinds of conflict, alliance, and peace. He is interested in the recurrence of certain patterns—fear, prestige, security dilemmas, the search for allies, the temptation to exploit weakness—but he refuses to reduce history to a single mechanism.
War is treated as a social and political institution, not simply as a breakdown of order. Aron follows the Clausewitzian insight that war is a continuation of politics by other means, while also insisting that war has its own logic and can escape the intentions of those who begin it. He examines the variety of wars—wars of conquest, wars of prestige, wars of ideology, wars of national liberation, and wars fought for security—and the ways in which political ends shape military means. He is equally concerned with peace. Peace is not a single condition. Aron distinguishes forms of peace such as peace through equilibrium, peace through law, peace through hegemony or empire, and, in the nuclear age, peace through terror. None of these is identical with justice, and none is guaranteed to last. Peace can coexist with oppression, inequality, and unresolved conflict.
A substantial part of the book concerns the nuclear age. Aron analyzes deterrence, the thermonuclear stalemate, and the paradoxes of strategic rationality. Nuclear weapons make total war between great powers potentially suicidal and therefore transform the relationship between force and diplomacy. But they do not abolish politics. Limited wars, subversion, propaganda, economic pressure, and political competition continue. Deterrence may preserve a kind of peace, but it is a fragile and morally troubling peace, resting on the threat of massive destruction. Aron is neither a nuclear utopian nor a fatalist; he examines how strategic doctrine, political ends, and moral responsibility interact in a world where the use of force is both ever-present and potentially catastrophic.
The book also considers the ends of foreign policy. States pursue security, power, prestige, and ideas, but these goals are often mixed and ambiguous. Aron rejects the notion that states can be understood only as power-maximizing machines. Ideology, nationalism, domestic politics, and conceptions of legitimacy shape what states want and how they pursue it. At the same time, he rejects the opposite extreme that would explain international politics solely through domestic ideology or economic structure. Politics has its own autonomy, and the international system has effects that no single state can control.
Aron’s treatment of morality is especially important. He refuses both a purely Machiavellian realism that dismisses ethics and a Kantian idealism that ignores the responsibilities of political action. The statesman must act in a world of consequences, compromise, and incomplete knowledge; prudence is a political virtue. But prudence is not the same as cynicism. Aron insists that moral judgment remains relevant, even if the relevant morality is not a simple rule-following morality. The statesman is responsible for the survival and welfare of a community, and that responsibility may require choices that are morally costly. The book explores this tension rather than dissolving it.
The work is also a critique of would-be sciences of international relations that promise prediction. Aron’s theory is conceptual and historical: it seeks to clarify the basic structures of international action, to identify recurrent dilemmas, and to make historical comparison possible. It does not claim to produce laws from which particular wars or peace settlements can be deduced. His method is closer to historical sociology and political philosophy than to behavioral prediction. He is interested in understanding the meaning that actors give to their conduct, the institutional contexts in which they act, and the range of possible choices open to them.
Throughout, Aron returns to the antinomies of international life: sovereignty versus international law, power versus justice, prudence versus principle, the state as a moral community versus the state as an egoistic actor, and the desire for peace versus the persistence of conflict. The book does not resolve these antinomies in a simple formula. Its achievement is to map them with historical depth and analytical precision, showing why international politics is neither a realm of pure power politics nor a domain that can be easily moralized or legalized out of its central dilemmas.
The book’s central analytical distinction is between the international system and transnational society. The international system is composed of political units—primarily states—that maintain regular relations and retain the capacity to resort to force; transnational society consists of cross-border exchanges, loyalties, organizations, and solidarities that cut across those units. Aron treats the two as interwoven rather than separate: transnational ties can soften or complicate interstate rivalry, while the competitive logic of the system can reshape or suppress them. This distinction allows the book to treat international relations as a distinct domain without reducing it either to state power alone or to global social forces.
Within the system, the book attends to the configuration of power and to the homogeneity or heterogeneity of its members. Systems differ according to how power is distributed among poles and according to whether the units share basic conceptions of legitimacy, regime, and acceptable conduct. Homogeneous systems do not eliminate conflict, but they alter its meaning and limits; heterogeneous systems make ideological suspicion and contests over legitimacy central. This framework permits historical comparison without pretending to predict particular wars or settlements.
Aron also treats strategy and diplomacy as the characteristic instruments through which states relate means to ends. Strategy is not merely the conduct of war but the organization of force in view of political ends; diplomacy is the continuous management of alignments, threats, and settlements. The book examines how military means, alliances, economic pressure, and ideological appeal are combined, and how the choice of means reacts back on political goals. It thus keeps the reciprocal relation between war and politics at the center, in a Clausewitzian spirit, while adapting that relation to a world of nuclear weapons and mass ideological conflict.
Another theme is the plurality of peace. Peace is not simply the absence of war or the victory of law; it can rest on balance, hegemony, shared norms, or exhaustion and fear. Aron treats these forms as unstable and morally ambiguous, because each embodies different costs and different distributions of power. The book’s significance lies in this combination of conceptual rigor and historical awareness: it offers a vocabulary for comparing international systems, for analyzing the mixture of force and consent, and for resisting both the reduction of politics to strategy and the moralization of strategy without political responsibility.
