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 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 introductory chapter presents some fundamental concepts that lay the foundation for the rest of the book. It seeks to accomplish three goals. First, it discusses the nature of war, and in particular Clausewitz’s dictum that war is politics by other means. It is stressed that the book employs a very broad concept of war, including conflicts between states, civil wars, terrorism, some forms of interpersonal violence, and others. Second, it considers the possibility that the practice and frequency of war have changed over time. It observes how some modes of warfare have changed and some have not. It also suggests that it may be premature to celebrate the end of war, or even the significant decline of war. Third, it describes the scientific approach to understanding war and peace, highlighting the importance of asking general questions, developing theoretical answers to those questions, and testing those answers with empirical data. It also defines concepts such as hypotheses, independent variables, and dependent variables, and describes different kinds of data that can be used to test war-related hypotheses.

International alliances are the most important security institutions in international relations. This chapter examines different types of alliances, including security pacts, nonaggression agreements, and consultation pacts. It then connects alliances to more established ideas about balance of power dynamics. The next part of the discussion centers on the question, why do we observe states complying with alliance agreements, under conditions of international anarchy? Some possible answers are: some international alliance treaties increase coalition fighting power; states and leaders risk paying international and domestic audience costs if they violate the terms of an alliance agreement; and states only sign alliance treaties they mean to comply with, which means they are deliberate in how they design alliance treaties. Other concepts and debates under discussion include balancing, hands-tying, bandwagoning, free-riding, military bases, and power projection. Many of these concepts are applied to a quantitative study on whether the presence of an alliance agreement makes a state more likely to intervene on behalf of another state, and a case study of World War I.

Measurement replication is the ability to replicate a study’s recorded measurements, using the original study’s same measurement parameters or coding rules, the same research design, and the original sample of the same population. Measurement replication is an important element of replication writ large and is essential for knowledge accumulation, since failure to replicate measurement casts doubt on the internal validity of a studies based on those data. Measurement replication is equally important for both quantitative and qualitative scholarly research, having revealed measurement errors in both types of research. This chapter argues for the continued need for measurement replication for exposing errors in fact, interpretation and context, and consistency of application.