This chapter examines the connections between sex, gender, and violence. It gives readers a basic introduction to the concepts of the biological category of sex, and the social category of gender, and how sex and gender relate to each other. It examines whether sex category factors such as testosterone levels and upper body strength affect propensities for violence. It identifies a number of factors connecting social and political structures pertaining to sex and gender – including the first political order, patriarchy, brideprice, polygyny, marriage market obstruction, militarized masculinity and the political repression of women – to various forms of violence, including wars between states, civil wars, terrorism, insurgency, violence against women, honor killings, selective abortion and infanticide, and sexual assault. It applies many of these concepts to a quantitative study examining when peacekeeping troops engage in sexual exploitation and abuse, and also to a case study of India. Last, it considers potential policy solutions to sex and gender repression and inequality, and to violence caused by them.

This chapter examines the causes, prosecution, outcomes, and consequences of civil wars. It defines the concept of civil war, distinguishes between nationalist and secessionist civil wars, and presents several factors thought to drive civil war onset, including grievance, relative deprivation, identity, lootable resources, and state capacity. It then examines factors that might affect the likelihood of ending civil wars once started, including whether the issues under dispute are seen to be indivisible and the severity of commitment problems. It describes the consequences when rebel groups fighting a civil war are fragmented, and relatedly when there are several actors fighting in a civil war. The chapter then lays out possible solutions for ending civil wars and creating lasting peace, including third-party guarantors, power-sharing, and creating integrated police and security forces. It then discusses some of the devastating human consequences of civil wars The chapter applies many of the concepts in the chapter to a quantitative study on whether peacekeepers help prevent civil wars from recurring, and a case study of the Syrian Civil War.

This chapter explores third-party mediation and peacekeeping. Mediation, along with arbitration and adjudication, is a form of peacemaking. Peacekeeping means maintaining durable peace after conflict has ended. The UN is one of several kinds of actors that engage in peacekeeping missions. They leverage the costs belligerents would pay if they return to war, provide information, reduce uncertainty, and provide political cover to facilitate political concessions. Also discussed in the chapter are peacebuilding efforts, including developing the proper political, legal, social and economic infrastructure to stabilize the security environment. Challenges for third parties seeking to engage successfully in peacekeeping and peacemaking include the difficulties they face in providing long-term incentives for peace, the possibility of distorting information flows such that peace is less stable, and being sensitive to local contexts. The chapter applies many of its concepts to a quantitative study of the causes of peacekeeper sexual exploitation and abuse, and a case study of third-party involvement during the conflicts in the Great Lakes region of Africa in the 1990s and 2000s.

This chapter examines the effects that individual leaders have in shaping foreign policy, including decisions for war. It first presents general international relations debates about whether international structure makes leaders irrelevant, or if instead leaders can make a difference. It then examines regular and irregular processes by which leaders can come to power. Then it describes how differences among leaders might translate into different patterns of foreign policy decisionmaking, including differences regarding beliefs and ideology, background experiences, sex and gender, personal health, and age. It also examines how variance in domestic politics – including the role of political parties, bureaucracy, and the firmness of a leader’s hold on power – can affect how and whether leaders can affect foreign policy choices, The chapter also discusses other concepts and debates, including the diversionary theory of war and whether reputation resides in leaders or in states. It then applies several of these concepts to a quantitative study on whether leaders who are former rebels are more likely to acquire nuclear weapons, and a case study on leaders and the causes of World War I.

This chapter presents the bargaining model of war. The basic approach of the bargaining model is to frame the onset, prosecution, and termination of war as a bargaining process: war represents a failure of two sides to reach a peaceful bargain settling a dispute over an issue such as a territorial border, and during war states continue to bargain, searching for a peace settlement both sides prefer over continuing to fight. Using very little math, the chapter introduces a number of key concepts, such as ideal points, reservation points, reversion outcomes, and bargaining space. It also lays out three possible bargaining model explanations as to why wars break out: when the sides disagree about the likely outcome of a war; when at least one side doubts the credibility of the other side to abide by commitments to peace; and when the issue under dispute is perceived to be indivisible. The chapter also develops information and commitment credibility perspectives on bargaining during wartime, and how wars eventually end. It applies these ideas to a summary of a quantitative study of the effects of peacekeeping on civil war outcomes, and to a case study of World War II in the Pacific.

This chapter explores the relationships between environmental stresses, natural resource shortages, and violent conflict. It describes ideas such as tragedy of the commons, carrying capacity, and common pool resources, as well as Malthusian theories. It also explains how environmental stresses can affect various kinds of conflict, through dynamics such as states sharing transboundary water resources clashing over maritime assets such as fishing and petrochemical reserves; resource shortages fueling conflicts over distribution among substate populations; and shortages causing internal migration, in turn fueling "sons of the soil" conflicts. It also describes how state capacity, rural economies, and groupness can affect the connection between environmental stresses and conflict. The chapter discusses how conflict can in turn exacerbate environmental stresses, and pays special attention to the consequences of climate change for conflict. The chapter applies many of these concepts to a quantitative study on the relationship between drought and conflict, and a case study on the role of drought in causing the Syrian Civil War.

This chapter discusses the economic dimensions of war. It begins with the classic guns vs. butter framework from economics, whereby spending on the military trades off with spending on other priorities. It builds on this concept to discuss the three main ways that governments finance wars, through increased taxation, borrowing, and printing money. It also examines the market for warriors – how governments gather citizens into the military as soldiers – comparing conscription and volunteerism systems. Next, it discusses the market for weapons, how the private sector produces weapons for the government, and the consequences of different market structures for weapons production. Among other concepts and issues, it explores the fundamental problem of sovereign finance (that government borrowers cannot be forced to pay off debts), the "commercial peace" proposition that trade between states breeds peace, and the economic consequences of war. It applies many of these concepts to a quantitative study on whether access to credit helps state win their wars, and a case study of the development of the US taxation system as a means to fund US participation in the World Wars.

Drone warfare is one of the most important trends in twenty-first-century conflict. This chapter surveys the history of drones – nonpiloted aircraft – and describes their basic features and how they differ from piloted aircraft and missiles. It assesses the advantages and disadvantages of using drones. The advantages include circumvention of some operational crew limitations; longer flight times; plausible deniability; and avoidance of friendly casualties. Whether drone strikes are effective, especially against terrorist and militant groups, is also considered. The chapter next works through the interwoven question of whether (certain types of) drone strikes are legal and/or ethical. It then turns to the political dimensions of how they are authorized, especially their implications for the separation of powers.The chapter then turns to the spread of drones to state and nonstate actors, and the frontiers in the future development of drone technology. The chapter applies many of these concepts to a quantitative study of whether drone strikes reduce terrorism, and a case study of US drone strikes on targets on Pakistani territory in the 2000s and 2010s.

This chapter describes the relationships between domestic political institutions and war. Moving beyond older debates comparing democracies and autocracies, it presents a conceptual structure for differentiating among different types of autocracies. Autocracies vary as either being personalist or non-personalist, and also as being led by either military officers or civilians. Personalist regimes are less constrained by domestic audience costs, and military leaders are more likely to embrace the effectiveness and legitimacy of using force. The likely onset and outcome of conflicts vary across autocracy types. The chapter explores other ideas linking domestic politics and war, including the diversionary theory of war, coup-proofing (when autocrats take steps to reduce their risk of being overthrown in a military coup d’état), and the marketplace of ideas (when foreign policy issues can be freely debated in government and society). The chapter applies many of these ideas to a quantitative study on what kinds of political systems are more likely to win their interstate wars, and a case study of Iraq’s 1990 invasion of Kuwait.