In his book, Michael Woldemariam explains the cohesion and fragmentation of insurgent groups, particularly Eritreans who fought a 30-year war for independence from Ethiopia. That hostility nominally ended in 1991, when the Eritrean People’s Liberation Front (EPLF) defeated Ethiopian forces in Eritrea. A referendum two years later formalized Eritrean statehood. However, cross-border tensions festered throughout the 1990s and early twenty-first century, claiming the lives of more than 80,000 people.

Many readers will probably turn to Insurgent Fragmentation in the Horn of Africa to grasp the background of a dramatic rapprochement in 2018. That July, Eritrea and Ethiopia finally reconciled after Ethiopian Prime Minister Abiy Ahmed announced that his government would “fully accept and implement” the terms of a 2000 peace treaty, the Algiers Agreement. Practically overnight, commercial flights resumed operation and telephone lines reopened between the countries; friends and relatives reunited after years of separation. On September 16, Abiy and Eritrean President Isaias Afwerki signed an accord at a ceremony in Saudi Arabia. Woldemariam’s book is indeed a handy primer on the intricate saga of war and peace in the Horn of Africa from the 1960s to recent times.

There is another reason why the book is timely, however: Only now, three decades after the Eritrean War of Independence and two decades after the Algiers Agreement, is it possible to correct “old, sanitized narratives, about the purity of the EPLF, its unity and coherence, and the unquestioned integrity of its leadership” (p. x). In general, political scientists are not in the best position to objectively analyze a conflict while passions still run high, especially if they are familiar with the context by virtue of having participated in or witnessed key events (or knowing people who have). Woldemariam discloses in the acknowledgments that he is the son of refugees who fled Eritrea’s independence struggle. He thus embodies a balance between proximity and distance (both spatial and temporal) that is rare in political science. He regards 2001 as a juncture where public opinion turned against the EPLF, which had refashioned itself from a liberator into a ruling party. He writes that “many began to call for a more honest, and perhaps more subversive, historical rendition of the independence struggle” (p. xi). The author is exceptionally qualified to deliver that rendition, availing himself of personal experience in the diaspora, hindsight, and a full social-scientific toolkit.

Woldemariam’s central research question also applies beyond the Horn of Africa, asking as he does why and under what conditions rebel organizations fragment. This puzzle is important if one assumes, as rebel leaders and civil-war scholars long have, that cohesive fighting units are more effective at winning power than divided units. His question is doubly significant in light of previous findings that rebel fragmentation shapes the intensity of violence (Jeremy Weinstein, Inside Rebellion, 2007), conflict duration (David E. Cunningham, “Veto Players and Civil War Duration,” American Journal of Political Science, 50(4), 2011), state failure (Christopher Clapham, ed., African Guerrillas, 1998), and postwar governance (Reyko Huang, The Wartime Origins of Democratization, 2016). The ideal audience for this monograph therefore encompasses military strategists, peace builders, and conflict experts working in an age when most wars are of the intrastate, as opposed to the interstate, variety. The book also concerns scholars of unarmed bodies, such as social movements, political parties, and corporations, which exhibit varying degrees of cohesion and fragmentation.

The author answers his research question with a counterintuitive hypothesis: Rebel fragmentation is least likely under a “cohesive stalemate,” where rebels are neither relinquishing nor gaining territory. Under those circumstances, the rebels believe they still have a chance to beat the state, but that the insurgency remains necessary because they have not won yet. By extension, fragmentation is more likely when rebels either lose or acquire territory.

The evidence for this hypothesis comes mainly in the form of process tracing, contained within two meticulous chapters on Eritrean rebel organizations and two shorter chapters on “shadow cases” of other insurgencies in the Horn (including groups in Somalia, which Woldemariam frames as a check of external validity despite not leaving the region). The empirical core of the book is a master class on how to motivate and implement a process-tracing approach. With the utmost care, he follows best practices for justifying his case selection, identifying observable implications of his theory and adjudicating between rival hypotheses. The result is a cogent test of his argument, although the level of detail this requires might prove daunting to nonspecialists.

Woldemariam conducted an astonishing amount of archival research and sometimes dangerous fieldwork for this book. Yet it is worth drawing attention to another impressive aspect of his project: an originally coded data set of rebel fragmentation in sub-Saharan Africa from 1946 to 2006, which will surely be of use to other scholars studying civil war. He codes fragmentation as splits resulting in the creation of new rebel organizations (though for reasons that are not entirely clear, he changes the definition in later chapters to include splits resulting in mergers with other rebel groups or with the incumbent government). The author uses the data set in Chapter 1 to illustrate the high prevalence and geographic variation of his dependent variable. In Chapter 2, he speeds through a cross-sectional, longitudinal regression analysis of fragmentation on a subset of data from Ethiopia, controlling only for gains or losses of territory and prior fragmentation. Even with a modest sample of 221 cases, it would have been feasible and interesting to estimate a more thoroughly specified model that might have corroborated the subsequent qualitative analysis. Woldemariam could also have expanded his entire Africa-wide data set into a panel format, permitting more complex statistical modeling.

In fairness, most publishers limit the number of pages an author can write. Woldemariam chose to allocate most of his pages to thick description, and his book is better for it. Much of the literature on civil wars, especially from the 1990s, uses large-n data sets and therefore obscures micro-level phenomena like the thoughts and actions of individual combatants. Readers trained in that tradition of arm’s-length research will marvel at the intimacy of his interviews, such as one with a veteran insurgent in Eritrea who recounts, “I took the first bullet” in protracted battles over territorial claims (p. 116). This book’s comparative advantage is analytic depth, and so it would be unreasonable and counterproductive to ask Woldemariam to broaden his scope to incorporate the countless topics relating to rebellion. Other writers can and have contributed complementary perspectives—for instance, on insurgency beyond the Horn (e.g., see Jessica A. Stanton, Violence and Restraint in Civil War, 2016) and on the central role of female warriors in the EPLF (e.g., see Victoria Bernal, “From Warriors to Wives: Contradictions of Liberation and Development in Eritrea,” Northeast African Studies, 8(3), 2001).

Scholars of contentious politics share a delicate task of drawing policy implications from their findings that readers might construe as taking a side or justifying controversial foreign intervention. For example, my own book, Political Protest in Contemporary Africa (2018), concludes with a call for Western donors to pledge greater support to certain African activists without any guarantee that such engagement will improve well-being rather than backfire violently. Woldemariam’s book is no exception to the awkwardness of advising policymakers (implicitly, those in the West) on how to make risky choices in volatile settings. In his conclusion, he proposes that “coalition forces in Afghanistan could cede portions of southeastern Afghanistan to Taliban forces in order to incite internal unrest within what is an admittedly diverse organization” (p. 284). This counterinsurgent advice seems at odds with his recommendation on the next page, that peace negotiators try to prevent rebel fragmentation in order to help parties unite during peace talks (p. 285).

It is ambiguous whether the author is thinking aloud or sincerely addressing decision makers in Washington. Academics have a habit of conducting thought experiments, but they should be prepared for readers from military, intelligence, state, or development agencies to take their advice literally. In principle, it is good to have the ears of people in power. But in practice, this confers on scholars both an opportunity and a responsibility; officials who decide the global flow of money and material do not necessarily share the skepticism of scientists, but instead cherry-pick evidence that justifies their agendas and budgets (Aaron J. Abbarno and Nicole Bonoff, “Applied Political Science and Evidence-Based Foreign Assistance in Democracy, Human Rights, and Governance,” PS: Political Science and Politics, 51(3), 2018). De rigueur, political science books end with a list of policy implications. Our profession could benefit from more formal dialogue—in journals, on conference panels, and elsewhere—about how to translate scholarly findings for practitioners. Woldemariam would undoubtedly lend valuable insights to the conversation.

The overall value of this book is to look backward as well as forward at civil war in the Horn of Africa and beyond. The author first paints a full and realistic picture of the EPLF, refining its image as a liberating party. Then, drawing on lessons from the past about when and why rebel groups fragment, he proposes several possibilities for future conflict resolution. All of these policy solutions, whether they involve facilitating or averting rebel fragmentation, require peacemakers to seriously engage with rebels under conditions where the only certainty is that there will be winners and losers. Woldemariam guides this precarious work by revealing how rebels strategize when they undergo gains and setbacks.