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.

This chapter explores terrorism, terrorist groups, and potential solutions to terrorism. It discusses conceptual and legal definitions of terrorism. It then provides historical context, describing terrorist waves driven by ideologies such as anarchism, anti-colonialism, New Left perspectives, and various religions. The chapter looks at who becomes a terrorist, taking account of theories of grievance, radicalization, recruitment by terrorist groups, lone wolf terrorism, and foreign fighter recruitment. It considers relationships between regime type and terrorism, examining why democracies, anocracies, and autocracies respectively might be more or less likely to attract terrorist violence, and exploring issues such as media coverage, grievance, and repression. Terrorist tactics and how these might diffuse across groups are discussed, as are terrorist group cooperation and state sponsorship of terrorism. The chapter also looks at the challenges of crafting effective counterterrorism policy, with a focus on deradicalization. It then applies many of these concepts to a quantitative study on whether targeting terrorist group leaders helps stop terrorism, and a case study of al-Qaeda.

This chapter opens with some basic description of and historical background on nuclear weapons. It then develops the basics of nuclear deterrence theory, working through concepts such as mutual assured destruction, first strike capability, second strike capability, first strike instability, the stability–instability paradox, and the nuclear triad. It then works through the causes of nuclear proliferation – the spread of nuclear weapons to new countries – including the logistical details of starting a nuclear weapons program. Relatedly, it examines the tools the international community possesses to slow the spread of nuclear weapons, including the Nuclear Non-Proliferation Treaty, extended deterrence, and economic sanctions, before working through both sides of the debate on whether the spread of nuclear weapons is stabilizing or dangerous. It then asks if nuclear weapons are useful tools of interstate coercion, before examining the conceptual foundations and history of nuclear arms control. The chapter applies many of its concepts to a quantitative study of whether extended deterrence makes allies more likely to start wars, and a case study of North Korea’s nuclear weapons program.

This chapter examines the role public opinion plays in the formation of foreign policy, especially decisions for war. It first presents foundational concepts and debates about the nature of public opinion, including the conditions necessary for the public to have reasoned judgment about foreign policy, and the conditions necessary for public opinion to affect foreign policy in a democracy. It then examines a series of related issues and debates, including whether the public holds coherent opinions, how the public uses information to form opinions, the role of the media in the formation of public opinion, and whether public opinion is shaped by the spin of political elites. It explores the role of partisanship in public opinion, and tackles the normative question of whether public opinion should guide foreign policy choices. It addresses other concepts pertinent to public opinion debates, including framing, the elasticity of reality, and "rally ‘round the flag" effects. It then applies many of these concepts to a quantitative study of the effects of battlefield events and leadership rhetoric on public support for war, and a case study of public opinion during the Iraq War.

Agents in real environments are inevitably forced to make decisions based on incomplete information. Even when an agent senses the world to find out more information, it rarely finds out the exact state of the world. For example, a doctor does not know exactly what is going on inside a patient, a teacher does not know exactly what a student understands, and a robot does not know what is in a room it left a few minutes ago.

The previous chapter discussed how an agent perceives and acts, but not how its goals affect its actions. An agent could be programmed to act in the world to achieve a fixed goal or set of goals, but then it would not adapt to changing goals, and so would not be intelligent. An intelligent agent needs to reason about its abilities and goals to determine what to do.

Once the Court has established that an interference with a Convention right meets the requirement of lawfulness, the second main requirement for the interference to be justifiable is that it pursues a legitimate aim. The express limitation clauses of the Convention further do not only require the aims pursued to be legitimate, but they also provide exhaustive lists of the aims which can legitimately be served. Although the test of legitimate aim does not play a large role in the Court’s review of justification for restrictions, this Chapter addresses the application and interpretation of the legitimate aim requirement. Special attention is paid to the situation of a discrepancy between stated and real aims and the situation where more than one aim is pursued. In addition, Article 18 ECHR is discussed, which states that restrictions cannot be applied for any other purpose than that for which they have been prescribed. The Merabishvili case and the requirements defined therein are central to this discussion.

An agent that is not omniscient cannot just plan a fixed sequence of steps, as was assumed in Chapter 6. Planning must take into account the fact that an agent in the real world does not know what will actually happen when it acts, nor what it will observe in the future. An agent should plan to react to its environment.

This chapter shows how an intelligent agent can perceive, reason, and act over time in an environment. In particular, it considers the internal structure of an agent. As Simon points out in the quote above, hierarchical decomposition is an important part of the design of complex systems such as intelligent agents.

The previous chapter assumed that the input were features; you might wonder where the features come from. The inputs to real-world agents are diverse, including pixels from cameras, sound waves from microphones, or character sequences from web requests. Using these directly as inputs to the methods from the previous chapter often does not work well; useful features need to be created from the raw inputs.