The siege of a city or a huge defensive stand appears archaic in the modern battlefield. With modern armed forces possessing weaponry that has more firepower and precision than at any time in history, decisive battles should be the norm in wars. Indeed, the term “siege” conjures images of defensive stand-offs in the Middle Ages. Yet Peter Andreas's book reminds us that military sieges have contemporary relevance.

Blue Helmets and Black Markets examines the imposition, maintenance, lifting, and aftermath of the siege of Sarajevo, which lasted from April 1992 to February 1996 and was the longest in the history of modern warfare. How did the city survive and defend itself for such a long period of time? Andreas argues that the siege of Sarajevo was unique not only because of its exceptional length but also because of its highly internationalized character. For a besieged city, Sarajevo was remarkably open and porous. The ostensibly “barricaded” city drew in large numbers of foreign aid workers, diplomats, United Nations peacekeepers, journalists, and black market traders. Humanitarian aid and military resources also moved into the city relatively unfettered.

The book demonstrates how the internationalization of the Sarajevo siege, which was aimed primarily at ending the conflict, actually helped to prolong it by creating a war economy in which an unintended symbiotic relationship developed among the besiegers (Serbians), the besieged (Bosnians), and the external interveners (UN and western countries). The permeability of the city made the siege politically tolerable, militarily acceptable, and economically profitable for the key players. Over time, it became less about defending the city or achieving a decisive military victory and more about the control of humanitarian supplies and smuggling routes in and out of the city. While a majority of Sarajevo's inhabitants struggled to survive, the flow of supplies (both humanitarian and military) served the narrow political interests on both sides of the civil conflict. For the Serb besiegers, the blockade helped distract the international community from the far more severe atrocities they were committing elsewhere in the conflict. For Sarajevo's political leadership, the siege created an environment that allowed party leaders to enrich themselves and marginalize political opponents through their control of black market supplies. For the UN and Western countries, the siege was a showcase of post–Cold War humanitarian assistance.

Chapters 2 and 3 are probably the most important. They focus on the buildup to the siege, its imposition and persistence, and the way it in effect institutionalized Sarajevo's war economy. Three developments were crucial in this regard. First, the siege raised the stature of Sarajevo's criminal networks. Before the arrival of the international peacekeepers and in the absence of a credible defensive system, Sarajevo's political leaders turned to the city's criminal groups for assistance. Second, because of the shortfall in official humanitarian assistance, the UN and Western countries condoned the rise of a black market trade that crossed siege lines. Third, vital military equipment and supplies gradually filtered into the city often with the complicity of the international peacekeepers and the Serbian besiegers.

This is an enjoyable read. Andreas tells a compelling story, one that is accessible even for readers who have little background knowledge of the Balkans. The book contains extensive primary source material, drawn from in-depth interviews and an extensive list of vernacular and international media sources, official testimonies, government documents, court transcripts, war diaries, and memos. For political scientists, this is a timely reminder that sieges should not be just the purview of military historians and analysts. The author demonstrates that the siege of a city—its imposition and maintenance—can have profound political implications. Using the extent of internationalization as the key variable, he helps us understand why certain sieges were short-lived while others were just as long-lasting as Sarajevo. He nicely summarizes some of these findings in Chapter 7, which compares the Sarajevo siege with other besieged cities such as Srebrenica, Leningrad, Grozny, and Falluja.

Blue Helmets and Black Markets revisits the argument of Charles Tilly's War Making and State Making as Organized Crime (1985)—that the process of war making profoundly shapes states and their economies. Andreas demonstrates that Tilly's argument, while focused on premodern Europe, has continuing contemporary relevance. He demonstrates that in Sarajevo, the close relationship between politicians and criminal networks led to rampant criminalization and corruption and impeded efforts at political reform during the postwar reconstruction period. In doing so, he highlights the importance of thinking about how the business of war making intersects with the business of crime. At the same time, the complicity of the UN and other international aid agencies in creating and sustaining the black market and other illicit activities during Sarajevo's siege highlights the need to look beyond the stylized image that humanitarian interventions can do no wrong. The book shows that international humanitarian interventions in conflict zones can shape and become part of illicit war economies.

Andreas's argument that the internationalization of the Sarajevo siege inadvertently prolonged the city's lockdown also offers fresh insights into why the broader Bosnian civil war lasted as long as it did. While most existing studies of civil war duration typically focus on factors internal to the state—such as bargaining and credible commitments between the warring factions—Andreas's internationalization argument explores how the external dimensions of civil conflicts can explain their persistence.

Despite these strong contributions, the book has two major flaws. First, it is insufficiently clear how and where this study fits into the wider theoretical debates within political science. While it may have been written to be accessible to readers with a wide array of interests, including humanitarian interventions, civil wars, or even political economy, it does little to advance serious scholarly analyses of any of the aforementioned issues. Take, for instance, the topic of humanitarian interventions. While Andreas cites the UN's complicity in the creation and maintenance of Sarajevo's black market in order to warn us that humanitarian interventions could have deleterious consequences if there are no adequate oversight mechanisms, he fails to push the implications of this argument further. Several corollary questions emerge from this finding: How should the international community better manage humanitarian interventions? What oversight mechanisms should be in place? Is it not possible that humanitarian interventions actually prolong civil conflicts? Under what conditions will humanitarian interventions prolong a conflict and under what conditions will conflicts prolong interventions? The author fails to mention, much less discuss, serious questions such as these. Part of the reason no doubt relates to the book's atheoretical bent. Its main contribution is its process tracing of the siege of Sarajevo. Process tracing helps explain “how” questions: How was the siege imposed? How was it maintained? How was the siege lifted? It is less useful, however, for answering why questions.

The book's implicit argument is that the self-interests of the actors in the civil conflict kept the siege going. For example, the UN collaborated with the besiegers and black marketers because their interest was to ensure that aid got into the besieged city. Politicians in Sarajevo teamed up with criminals in order to remain in power and accumulate wealth. While these may have been accurate depictions of these actors' motivations, “self-interests” do not explain why the most important causal process described in the book—the internationalization and then institutionalization of Sarajevo's war economy—came about. Had Andreas been more rigorous in his understanding of the advantages and limits of process tracing, and had he also drawn upon principal-agent theory and other more systematic approaches to the study of collective action and civil violence, he would have been able to offer a stronger explanation of why the Sarajevo war economy developed and persisted as it did, and how in doing so it contributed to the duration of one of the most vicious and consequential conflicts of the post–Cold War world.