The Arc of War

–by William R. Thompson      

           Forecasting the level of conflict two decades ahead is not something we political scientists are very good at – in part because we lack appropriate theories and in part because it is hard to tell how the world will look in the future.  The 2030 report appears to use a combination of projecting current trends and relying on some key indicators such as demographics to predict declining or no conflict between great powers, states in general, and within states, subject to some reservations about the possible impact of climate deterioration, resource scarcities, ascending powers, and new weapons.       

       I would probably make a similar but not identical projection based on different theoretical premises.  My forecast would be based on arguments developed in The Arc of War (University of Chicago Press, 2011), an examination of the evolution of warfare since its initial appearance and co-authored with Jack S. Levy.   Levy and Thompson make six general arguments.  The first one is about the origins of war and need not concern us here.  The other five do appear to be germane.

  1. War co-evolves with other activities, including military and political organization, political economy, threat environment, and weaponry.
  2. Major changes in politico-economic complexity, in particular have led to occasional transformations in warfare.  Yet, the expansion of warfare is not inexorable. An important constraint in the escalation of warfare are its costs which have influenced strongly and negatively the probability of warfare between industrialized states in the contemporary era.
  3. The pace of change/transformations in warfare 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.
  4. 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.
  5. Much of the world did not experience the third acceleration directly (other than as targets) and remains more agrarian than industrial.  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.

       Thus, warfare between industrialized major powers should continue to be regarded as too costly and therefore not very likely in the next few decades.  Interstate warfare should also continue to be infrequent mainly because most states lack the resources to engage in it for very long.   But we would expect intrastate warfare to continue more or less at current levels because so many states are vulnerable to coercive challenges at the domestic level.  Since drought and oil/water shortages seem likely and most likely to occur in places that are least able to cope with such problems, anticipating limited interstate warfare may prove to be optimistic.  But the increased problems caused by climate and scarcities may at least tell us which parts of the world are most likely to experience conflict in the near future.


William R. Thompson is Distinguished Professor and Donald A. Rogers Professor of Political Science at Indiana University, Bloomington.  He also is Managing Editor of International Studies Quarterly. Recent books include Asian Rivalries: Conflict, Escalation, and Limitations on Two-Level Games, Handbook of International Rivalries, 1494-2010, and The Arc of War: Origins, Escalation and Transformation.  Forthcoming next year are How Rivalries End and Transition Scenarios: China and the United States in the Twenty-first Century.

By allandafoe Posted in GT2030

Will the Long Peace Persist?

We live during an era of historically unprecedented peace. Whether we look over timescales of decades or centuries, wars have become less frequent. Figure 1 (data drawn from Pinker’s excellent new book, original sources include here and here) illustrates the downward trend in five measures. There are fewer Great Power wars, fewer wars in Western Europe, fewer years during which a Great Power war is ongoing, and less redistribution of territory after wars. Other trends, not as readily quantified, are evident. Countries no longer covet each other’s territory, or fear invasion and military coercion, like they have throughout most of history. National identities and aspirations are based less on martial glory, honor, and dominance. The relative absence of war, and especially Great Power war, since the end of WWII has been referred to as the Long Peace. As unbelievable as it may seem to readers of history, these and other trends suggest to many scholars that the Long Peace is likely to persist. 

Figure 1




But unlike the robust decline in interpersonal and domestic governmental violence (again, see Pinker), it is not as obvious that the human costs of war have declined over time. Figure 2 illustrates two other important measures that don’t show a decline: except for the most recent few decades, battle deaths in Great Power wars and battle deaths as a proportion of population in Europe don’t show an obvious decrease. While recent decades do seem particularly peaceful given these long-term trends, we would hardly want to be complacent about this trend. Many previous decade-long spans of peace ended in devastating wars. 

Figure 2


It may be, then, that wars have become vastly more destructive, especially with the invention of nuclear weapons, leading countries to be more cautious about their use of military coercion. The net costs of war on humanity, however, may not have decreased. The Cuban Missile Crisis ended with little bloodshed; however, it could have ended with hundreds of millions of deaths. Such a counterfactual would add a massive spike to the right end of the lines in Figure 2, and mute any discussion of a Long Peace.  

Aggregate data like the above gives us some, but not a lot, of confidence that the world has moved beyond war. To probe the persistence of this Long Peace, it would be helpful to know what factors have made the world more peaceful, and the extent to which these factors are likely to persist into the future. Potential causes of the peace include increases in trade, democracy, the difficulty of coercing wealth, global empathy, Great Power stability, the empowerment of women, and the deterrent effects of nuclear weapons. Global Trends 2030 identifies a number of other factors pertinent to the future probability of war, including power transitions, declining US military superiority, resource scarcity, new coercive technologies (such as cyberweapons, precision-strike capability, and bioweapons), and unresolved regional conflicts. 

Wars are rare, but when they occur they alter the course of history. Any projection of what the world will be like decades into the future needs to evaluate the probability and character of war, and especially Great Power war. This week we can look forward to a set of eminent scholars sharing their thoughts about whether the Long Peace will persist. Contributors include: Erik Gartzke, (UC San Diego), Benjamin Fordham (Binghamton), Joshua Goldstein (American), Steven Pinker (Harvard), Jack S. Levy (Rutgers), Richard Rosecrance (Harvard), Bradley Thayer (Baylor), and William Thompson (Indiana).



Allan Dafoe is Assistant Professor of Political Science at Yale University. His research examines the causes of war, with emphases on the character and causes of the liberal peace, reputational phenomena such as honor and tests of resolve, and escalation dynamics. 



Pinker, S. 2011. The Better Angels of Our Nature: Why Violence Has Declined. Penguin Group. 

Levy, J. S., & Thompson, W. R. 2011. The Arc of War: Origins, Escalation, and Transformation. Chicago: University of Chicago Press.

Levy, J. S. 1983. War in the Modern Great Power System 1495–1975. Lexington: University Press of Kentucky.

Long, W. J., & Brecke, P. 2003. War and Reconciliation: Reason and Emotion in Conflict Resolution. Cambridge, Mass.: MIT Press.

Zacher, M. W. 2001. The Territorial Integrity Norm: International Boundaries and the Use of Force. International Organization, 55, 215-250.