Richard Caplan’s Measuring Peace adds significantly and provocatively to a somewhat fractious and controversial but nevertheless enduring conversation about what peace is—conceptually, operationally, and practically—and about how we should study this crucial phenomenon. In doing this, Caplan not only provides a thorough review of the terrain but he also attempts to add to our knowledge about what influences the quality of peace through a mixed-method analysis.

Rightly, Measuring Peace argues that existing scholarship on peace is something of a mess. Historically, different scholars have different orientations (i.e., very narrow/minimal as opposed to very encompassing/maximum). They also highlight distinct components (i.e., objectivity/subjectivity, politics/economics/society, and behavior/attitudes) with very little connections being made between the ever-widening chasms created by such practices or attempts to work through how the distances between these concepts could be traversed.

The book makes the case that in many ways those involved with peace building are not much better than academics. Here, Caplan notes that concepts of what peace is (if addressed at all) vary significantly across institutions but are essentially embodied within the activities of the relevant organizations themselves. Instructively, he works through the particularities of how some of these ideas find their way into actual policies of the African Union, the World Bank, and NATO. This, in my opinion, is where Caplan is at his best. Indeed, the discussions about the institutions and his reflections on “benchmarking” and “conflict analysis” are insightful about how diverse actors are innovatively addressing the difficulties with nailing down the elusive concept of peace.

Measuring Peace (again rightly) maintains that those involved with generating measures for peace are also all over the place. Relevant actors highlight politics, economics, and society at different levels of analysis and of empirical sophistication.

With this complexity as backdrop, Caplan tries to move the literature and broader policy field forward by distilling what he finds to be most critical about peace, how we could evaluate it, and what accounts for its variation. For example, he maintains that it is essential to move beyond the simplistic notion that ending overt military engagement (i.e., “negative peace”) is sufficient. In particular, he maintains that it is important to measure the quality of peace and the length of time that it is sustained. Caplan does give some attention to the diverse opinions about what peace is, drawing distinctions between more local/proximate and distant opinions and moving across levels of analysis (i.e., micro, meso, and macro), but these distinctions are not as effectively drawn out.

The quality and duration of peace are examined explicitly (in part with Anke Hoeffler). First, Caplan offers a quantitative analysis regarding all “peace spell durations” from 1990–2013; that is, how long a country went without a recurrence of armed conflict as defined/measured by the Uppsala Conflict Data Program. He finds that military victories (especially when governments defeat rebels) and reaching peace agreements tend to facilitate longer periods of peace. A more focused analysis considers the impact of UN peacekeeping operations on peace duration. In this investigation, he finds no significant effect for peacekeeping efforts but on further inspection discerns that the specific personnel who are involved does matter: when observers are involved there is no impact, when troops are involved things are made worse, and when the police are involved things are generally better. Second, there is a brief comparative analysis of six cases: Burundi, El Salvador, Liberia, Nepal, Sierra Leone, and Timor-Leste. Although this comparison provides some insights into the causal mechanisms discussed, the level of detail offered in terms of how cases were constructed, what types of information were used, and how information was triangulated across sources makes it difficult to comment on.

Pushing the parameters of the literature in important ways, Measuring Peace is not without its limitations/problems. In particular, I highlight five points.

First, Caplan devotes a large part of the book to making the case that there is extensive variation in the conceptualization and measurement of peace in the literature. This complexity is further extended to those involved with implementing peace policy and with measuring the effectiveness of these efforts in terms of orientation and quality. Although useful in many ways, this turns out to be somewhat problematic because readers are not provided with much insight regarding what they should do with all of this variation. In short, no criteria are provided to help navigate the troubled waters of peace-related scholarship.

Second, there is something of a tension within the book that reflects the relevant literature and field itself. After going over the extensive variation within the literature, Caplan pivots to a statistical evaluation. However, in doing this, he notes,

The pivot is a difficult one because what the scholarly literature and policy-oriented community both seem to demand is a multidimensional, nuanced, innovative, and dynamic empirical investigation of peace, and this raises the bar with regard to any effort to deliver. It is not quite clear that any scholar could achieve what is desired here, especially ones who are tied to more conventional forms of investigation. In certain ways, this is where Caplan goes by focusing his quantitative assessment on the importance of paying attention to duration. Why do this? This direction essentially flattens the very concept of peace that he shows to be complex, and it is not quite clear why one would focus on this dimension instead of others, such as the type of peace, the depth of peace, sequences of peace development, or dynamic interactions between the various actors involved. Indeed, this selectivity is especially troubling given the care that Caplan shows in laying out all of the variation noted earlier. After we have seen the forest, focusing on a single tree makes less sense.

Third, Caplan never seems to take issue with the fact that a period that ends with military victory (a form of violence) is associated with a period where there is no military conflict. In a sense, he highlights the violent origins of peace. Given what peace scholarship and peacebuilding are generally interested in, this omission is problematic. Indeed, harkening back to some of the foundational work on peace that considers it to be a phenomenon where the very idea of overt conflict is not possible, asserting the violent origins of peace seems contradictory. Can peace be achieved out of the barrel of a gun or after a series of violent confrontations?

Fourth, digging further into the quantitative investigation, the analysis offered never properly situates the examination of 1990–2013 in a broader perspective. For example, it is generally understood that the incidence of civil wars declines over time, but it is not clear how the period examined within the book fits into this overarching global pattern or what an evaluation of correlates within this period would mean. We know that different technologies of war and spatial diffusion are involved with civil war, but neither of these factors is included in the investigation. Indeed, in many respects, the conflicts are portrayed as being geographically contained entities—the explanation offered is almost exclusively maintained within the territorial jurisdictions of interest. This seems to be missing an important factor. Relatedly, there are now standard robustness checks that are provided along with analyses, but none are found in the book (or online), which makes one wonder how well the findings stand up to alternative specifications. Clearly, not many readers want to wade through such material, and editors often discourage such a product, but the idea of varied and distinct accounts of what is taking place offered by Caplan makes it an essential exercise.

Finally, digging even further into the qualitative investigation, it is not clear why the cases were selected, and it is incredibly difficult to convey the history of a case in the short summary manner each is described. This is troubling because Caplan spends some time trying to highlight the importance of ethnography and bringing alternative voices and local knowledge forward. Indeed, would not alternative perceptions of start dates, motives, dynamics, crucial turning points, and termination points be part of the conflict itself? Dueling perceptions are central reasons why conflagrations emerge. How can a simple and uniform accounting then emerge? These issues are not addressed.

Given all this, where does Measuring Peace leave us? I suggest that it has taken us up to a decent height from which we can get a better sense of the immense amount of thought and effort involved with the study and implementation of peace. The book gives us an idea how we might better understand the valley below and some ideas about how to navigate through/around it. Yet at the same time, it leaves us unclear about whether the tools/paths provided are the best ones to follow and toward what end.