Peacekeeping has been one of the main conflict management tools used by the international community to restore or safeguard peace and security. Since 1948, the United Nations has established 70 peace operations and has substantially evolved, adopting approaches to peace that extend beyond purely military concerns. Indeed, the promises of peacekeeping as effective instrument of conflict reduction may, to some extent, explain the evolution toward multidimensional missions and the unprecedented number of peacekeepers deployed in the last decade. As consequence, the growing importance of peacekeeping effectiveness has sparked a new wave of research that empirically investigates whether and under which conditions UN peacekeeping works. Peacekeepers are mostly deployed in conflict or postconflict environments where violence is either ongoing or lingering. Thus, violence remains a priority for peace missions. Consequently, peacekeeping is deemed successful or effective according to whether it curbs conflict in several dimensions. Effective missions are those responsible for decreasing the intensity of battle violence, protecting civilians, and containing conflict diffusion and recurrence in the postwar phase. Each mission, however, is deployed in different contexts and operates under variable conditions that affect the operation’s capacity to influence conflict. Concerning mission features, peacekeeping success is more likely when large contingents are deployed under robust mandates. Mission type, size, and composition signal credible commitment from the international community and empower peacekeepers to halt violence while guaranteeing the implementation of peace agreements. These nuanced understandings of peacekeeping stem from the availability of new data on both conflict and peace operations at the national and subnational levels of analysis. Moreover, the empirical study of the effectiveness of peace operations has recently been flanked by simulation-based forecasting, field experiments, and surveys investigating local-level outcomes of peace missions. Unsurprisingly, the focus on violence and conflict outcomes as indicators of success is debatable. First, in dealing with violence, peacekeeping operations produce spillover effects that are largely neglected, such as refugee flows and terrorist violence. Second, given the wide range of functions performed by UN peacekeepers, including electoral assistance, economic reconstruction, and state building, it is reasonable to include these aspects when defining effectiveness. Third, and relatedly, no assessment of short- versus long-term implications of peacekeeping for political, social, and economic development in the host country has been forthcoming. While reducing infant mortality, inequality, and crime are not necessarily tasks for peacekeepers, it is vital to study whether and how UN missions may have shaped the quality of peace in host countries.

Research on UN peacekeeping operations has established that operations' size and composition affect peacekeeping success. However, we lack systematic data for evaluating whether variation in tasks assigned to UN peacekeeping mandates matters and what explains different configurations of mandated tasks in the first place. Drawing on UN Security Council resolutions that establish, extend, or revise mandates of 27 UN peacekeeping operations in Africa in the 1991–2017 period, the Peacekeeping Mandates (PEMA) dataset fills this gap. It records 41 distinct tasks, ranging from disarmament to reconciliation and electoral support. For each task, the PEMA dataset also distinguishes between three modalities of engagement (monitoring, assisting, and securing) and whether the task is requested or merely encouraged. To illustrate the usefulness of our data, we re-examine Hultman, Kathman, and Shannon’s (2013) analysis of operations’ ability to protect civilians. Our results show that host governments and rebel groups respond differently to civilian protection mandates.

Research shows that peacekeepers reduce conflict intensity; however, effects of deployment on nonpolitical violence are unknown. This article focuses on criminal violence and proposes a twofold mechanism to explain why peacekeeping missions, even when effectively reducing conflict, can inadvertently increase criminal violence. First, less conflict opens up economic opportunities (so-called peacekeeping economies) and provides operational security for organized crime, thus increasing violent competition among criminal groups. Second, demobilized combatants are vulnerable to turn to crime because of limited legal livelihood opportunities and their training in warfare. While UN troops may exacerbate these dynamics, UN police's peculiar role is likely to successfully contain criminal violence. Cross-national and subnational empirical analyses show that large UN military deployments result in higher homicide rates, whereas UN police, overall, moderate this collateral effect.

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