The Arc of War: Origins, Escalation, and Transformation

The Arc of War: Origins, Escalation, and Transformation

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In this far-reaching exploration of the evolution of warfare in human history, Jack S. Levy and William R. Thompson provide insight into the perennial questions of why and how humans fight. Beginning with the origins of warfare among foraging groups, The Arc of War draws on a wealth of empirical data to enhance our understanding of how war began and how it has changed over time. The authors point to the complex interaction of political economy, political and military organization, military technology, and the threat environment—all of which create changing incentives for states and other actors. They conclude that those actors that adapt survive, and those that do not are eliminated. In modern times, warfare between major powers has become exceedingly costly and therefore quite rare, while lesser powers are too weak to fight sustained and decisive wars or to prevent internal rebellions.   Conceptually innovative and historically sweeping, The Arc of War represents a significant contribution to the existing literature on warfare.

Product Details

ISBN-13: 9780226476278
Publisher: University of Chicago Press
Publication date: 08/26/2011
Sold by: Barnes & Noble
Format: NOOK Book
Pages: 280
File size: 3 MB

About the Author

Jack S. Levy is the Board of Governors’ Professor of Political Science at Rutgers University and coauthor, with William R. Thompson, of Causes of War. William R. Thompson is Distinguished Professor and the Donald A. Rogers Professor of Political Science at Indiana University. He is the author or coauthor of numerous books, among them Asian Rivalries, Coping with Terrorism, and Causes of War.

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The Arc of War

Origins, Escalation, and Transformation


Copyright © 2011 The University of Chicago
All right reserved.

ISBN: 978-0-226-47629-2

Chapter One

The Evolution of War

War is a persistent feature of world politics, but it is not a constant. It varies over time and space in frequency, duration, severity, causes, consequences, and other dimensions. War is a social practice adopted to achieve specific purposes, but those practices vary with changing political, economic, and social environments and with the goals and constraints induced by those environments. A complete understanding of war requires an explanation of how it originated and how it has evolved. If war has changed in form over time, we need to identify when, how, and why it changed. We also need to know how war influenced, and was influenced by, other institutions and processes. If we find that the likelihood of war has diminished, at least in some regions or within some groups, we need to explain war's selective transformation as a social practice.

Our primary, and admittedly immodest, aim in this book is to explain the origins, escalation, and transformation of warfare. Central to that aim is describing and explaining how war has coevolved with other factors such as political and military organization, threat environment, political economy, and weaponry. Thus the arc of war is the storyline of war traced over time and space. In elaborating and explaining the arc of war, we make six arguments.

1. War emerged in different places at different times depending on the presence and absence of critical factors, including the development of hunting/homicidal skills, group segmentation processes, and the interactions among increased organizational complexity, resource scarcity, and conflicts of interest.

2. War coevolved with other activities, including military and political organization, political economy, threat environment, and weaponry.

3. Major changes in politico-economic complexity, in particular, have led to occasional transformations in warfare. Weaponry has become more specialized and lethal. Military organizations have expanded. Political organizations have expanded to manage larger and more deadly military forces and more intensified threat environments. The expansion of warfare, however, has not been inexorable. An important constraint is the escalating cost of warfare, which has especially impacted the probability of warfare between industrial states.

4. The pace of change/transformations in warfare and related processes has significantly accelerated three times—first in the late fourth to early third millennium BCE, then in the last half of the first millennium BCE, and again in the second half of the second millennium CE.

5. The attempt to centralize regional political-military power is one of the major drivers of periods of acceleration and transformation, especially in the third acceleration, which was concentrated in the western trajectory.

6. Much of the world did not experience the third acceleration directly (other than as targets), and it remains more agrarian than industrialized. As a consequence, states outside of the western trajectory tend to be weaker, vulnerable to internal warfare, and prone to fight fewer and shorter interstate wars.

Figure 1.1 provides a succinct summary of our argument. In brief, war originated and coevolves with other activities. The pace of evolution and coevolution has been characterized by three periods of acceleration. The contemporary outcomes of these changes and transformations are twofold: (1) strong, industrialized states for which warfare with other strong industrialized states has become very expensive and, therefore, less probable; and (2) weaker, agrarian states that have not experienced the third acceleration in the same way, and that are more likely to engage in internal warfare than in external warfare.

Our primary aim in this book is to elaborate and test these arguments about the arc of war. We must begin, however, by answering some preliminary questions. Does war in fact change over time? Are there major turning points? With what factors does war evolve and coevolve? What are the causal links among these processes?

Changes in Warfare over Time

Any discussion of the origins of war and any description of changes of warfare over time must begin with a discussion of what war is. All war involves violence, as Carl von Clausewitz reminds us, but not all violence constitutes war. To say that war originated in a particular period of human history is not to say that life was entirely nonviolent prior to the advent of war.

We define war as sustained, coordinated violence between political organizations. We elaborate on this definition elsewhere (Levy and Thompson 010b, 5–11), but a few points are worth mentioning here. For one thing, the actors who engage in war are political organizations, so that our definition is broad enough to include violent conflicts between states, empires, city-states, ethnic groups, chiefdoms, tribes, and hunter-gather groups, as well as many types of violent conflicts within those groups. In addition, for violence to constitute warfare it must be organized and it must have some threshold of magnitude or severity. This is standard in treatments of war in political science and in other social sciences. We depart from some scholars, however, by not formally incorporating "political purpose" into the definition of war. Our definition is behavioral. If two or more political units engage in the sustained and coordinated use of violence, it is a war regardless of the motivations for the violence.

Although we believe that most wars are driven by political motivations, we prefer to leave that as an empirical question rather than to assert it by definition. One issue is that the use of military force can be motivated by interests of actors other than the political organization itself. Political leaders may resort to military force for the primary purpose of bolstering their domestic political support, and bureaucratic organizations may advocate war to serve their own parochial needs. We do not want to imply that coercive force always aims to advance the interests of the organization in whose name force is used.

A second issue is that we can imagine instances in which military force is used not to influence others to act in a way to advance one's own interests, or to advance those ends by taking or destroying resources, but instead out of nihilistic or at least nonpolitical motivations. Although we think that most terrorist acts are politically driven, we concede that some might be more nihilistic. Note, however, that even if individual terrorists act out of nihilism, they almost always work for terrorist organizations for whom terror is a calculated political act. One exception might be the release of the nerve gas sarin in the Tokyo subways in 1995 by Aum Shinrikyo, a religious sect that was fixated on the impending end of the earth.

Finally, we concede that some uses of military force may be driven by cultural rituals rather than by means-ends calculations to advance interests. This is one of the things that John Keegan (1993, 3) had in mind when he began chapter 1 of his A History of Warfare with the provocative anti-Clausewitzian statement that "war is not the continuation of policy by other means."

If war is defined as sustained, coordinated violence between political organizations, there is little evidence of war 50,000 years ago. Population sizes were small, political organization was restricted to the hierarchies of small bands, and their frequency of contact was limited. Weaponry was certainly available but its lethal effects were limited. Resource scarcity varied by location and by episodes of climate deterioration.

One caveat worth noting, however, is that the movement of the Homo sapiens species into areas earlier controlled by Neanderthals could well have generated incentives for something resembling interspecies warfare about 5,000 years ago (Otterbein 00 ). We know only that the Neanderthals ultimately were extinguished and that our own hominid species triumphed. It is certainly conceivable that this outcome involved bloodshed. Nicholas Wade (2006, 90–9) speculates that Homo sapiens' slow penetration of Europe, requiring some 15,000 years of "border skirmishes," was due in part to stubborn resistance on the part of Neanderthal groups unable to retreat without encroaching on neighboring Neanderthal territory.

Three assumptions underlie this speculation: (1) ancient hunter-gatherers tended to move into new territory to find new food sources and (2) to moderate overpopulation in their former habitats, and (3) the original occupants were fairly belligerent about defending home territories, given some fixed carrying capacity. None of these assumptions is implausible, and each is supported by much of what we do know about the interaction of hunting-gathering groups.

Note, however, that Wade emphasizes Neanderthal–Homo sapiens "border skirmishes" rather than "war." Just how sustained specific clashes might have been and whether they reflected the coordinated behavior of organized groups so as to satisfy our definition of war is anybody's guess. It is also possible that the two species had no or little contact and that Neanderthals disappeared because they could not cope with climate change and/or a shift in the nature of their customary food supply.

Whatever the Neanderthal–Homo sapiens relationship, there is reason to believe that organized violence began to take place on a limited and sporadic basis long ago. The probability of some rival hunting groups occasionally coming to blows was moderately high, though evidence is scarce. Evidence of warfare begins to accumulate, if only slowly at first, for the last ten thousand years (Keegan 199 , chap. ; Haas 1999; Cioffi-Revilla 000; Gat 006, chap. ). Mass burials of bodies with projectile wounds, fortifications, burned walls, and pictures of armed combat and soldiers begin to appear.

For the last five thousand years, evidence becomes more plentiful and reliable. Full-fledged armies with armor-wearing soldiers in infantry formations begin to appear (Ferrill 1997). Gradually these armies became larger in size and more lethal in weaponry. States and empires emerged, grew in size, and built larger armies, and their wars became more lethal and began to claim more resources and lives.

As we indicate in table 1.1, which focuses on major battles, estimated deaths per war more than doubled between the fifth century BCE and the fourteenth century CE, more than doubled again between the fourteenth and early nineteenth centuries CE, and then increased by as much as a factor of ten between the early nineteenth and twentieth centuries. To be sure, these battles are not necessarily representative of every battle occurring in that era, and substantial war-related deaths can result from many small engagements as well as from major battles (Pinker 011, chap. 6), but these battles are probably roughly representative in terms of the increases in war-related deaths over time.

There are various ways to depict these trends graphically. Figure 1. sketches one individual's (Eckhardt 1992) estimated enumeration of battle deaths over several thousand years. The estimates are definitely unreliable in the early part of the figure, but in general they correspond to the description advanced above.

Although the severity of warfare, defined in terms of the number of casualties, has increased dramatically over time throughout most of history, there is substantial evidence that the frequency of some types of war has declined. Admittedly, it is extraordinarily difficult to estimate long-term trends in the frequency of war (or most other events) spanning several millennia, given a certain historical myopia and a systematic tendency to undercount more temporally distant events (Payne 2004, 67–70; Pinker 2111, chap. 7). We have much greater confidence in identifying patterns involving wars between the most powerful states in the system in the more recent past, especially for the last five centuries of the modern era as defined by historians, because the prominence of those events means that they are less likely to be undercounted.

Figure 1. plots the frequency of wars between great or major powers per decade during the last five hundred years. If we look at quarter-century periods, we find that the number of wars occurring every twenty- five years averaged around 5.5 in the sixteenth century and dropped to 1.25 in the twentieth century. A great power war has not occurred for over a half century, marking the longest period of great power peace for at least five centuries. The trend in the severity of great power war, defined in terms of battle-related deaths, is precisely the opposite, as indicated in figure 1.4. Thus great power warfare has steadily increased in severity while declining in frequency.

In the contemporary twenty-first century, a World War III, should it occur, has some potential for eliminating a substantial proportion of life from the planet. Yet in this same era there are significant parts of the planet in which, for the first time in thousands of years, most forms of warfare are highly unlikely to occur. Western Europe, for instance, certainly no stranger to warfare in the past thousand years, seems unlikely to experience anything resembling conventional interstate warfare in the near future. We could make the same argument about North America, and, perhaps with a little less confidence, about most of South America. For some populations, then, warfare has become a more remote possibility than it once was.

At the same time warfare has been much more common in other parts of the world. Wars between states—in eastern Africa (Eritrea and Ethiopia), central Africa (Rwanda, Congo, Angola, among others), the Middle East (Arab-Israeli, Iran and Iraq, Iraq and the United States), and South Asia (India and Pakistan)—are all very recent events. Threats of war remain conspicuous in East Asia (Taiwan and the two Koreas).

Interstate war is only one form of warfare, however, and it is no longer the one that attracts the most attention. We also need to examine trends in intrastate war and "extrastate war" (defined as the colonial and imperial wars that were traditionally fought between European states and entities not formally recognized by the European powers). In figure 1.5 we plot the frequency of different kinds of wars during the last two centuries, with each data point indicating the number of wars in the following decade.

The onset of interstate warfare follows an irregular wavelike pattern over the last two hundred years since the Congress of Vienna in 1815. After nearly two decades without an interstate war from the late 1820s to the late 1840s, the frequency of interstate war increased through the 1860s, declined briefly before increasing for another four decades through World War I, declined and peaked again around World War II, and rose again in the 1960s and 1970s before declining rather steadily through the end of the twentieth century. The phenomenon of extrastate war follows a somewhat similar pattern, though with different peaks and valleys. It peaked at the end of the nineteenth century at the height of European colonial expansion, persisted through much of the twentieth century at a low level, before ceasing altogether by the end of the 1970s, after the collapse of colonial empires following World War II.

Intrastate warfare shares some of this rhythm, peaking in the 1860s, again around 1920, and again in the late 1980s after a sustained increase. What is different, however, is that while the number of new interstate wars declined precipitously after 1970 or so, the number of new intrastate wars increased or remained high in the last third of the twentieth century. Evidence suggests, however, that the frequency of intrastate war (and therefore all types of war, given the end of extrastate war and the relative infrequency of interstate war) began to decline in the 1990s (Hewitt, Wilkenfeld, and Gurr 2010; Human Security Centre 2005; Harbom and Sundberg 2009; Sarkees and Wayman 2010). Despite a more recent increase in intrastate war, the decline in the 1990s helped to trigger a lively debate about the possibility of a sustained decline in war and perhaps in other forms of violence as well (Gleditsch 2008; Pinker 2011).


Excerpted from The Arc of War by JACK S. LEVY WILLIAM R. THOMPSON Copyright © 2011 by The University of Chicago. Excerpted by permission of THE UNIVERSITY OF CHICAGO PRESS. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents

List of Tables and Figures

Chapter 1. The Evolution of War
Chapter 2. The Origins of War
Chapter 3. Evolutionary and Coevolutionary Processes
Chapter 4. The First Two Agrarian Warfare Accelerations
Chapter 5. The Third Evolutionary Acceleration
Chapter 6. The Coevolution of the Western Military Trajectory
Chapter 7. Nonwestern Military Trajectories
Chapter 8. The Coevolution of War, Past and Future


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