In this chapter, students will learn about postcolonialism as an increasingly prominent theoretical approach to security in International Relations (IR). Focussing on the legacy of empire and the perpetuation of hierarchies between the Global North and South, postcolonialism is best understood as an orientation rather than one coherent theory, or even a cohesive school of thought. Postcolonial thought is inherently interdisciplinary and while there is no postcolonial school of security studies, it nonetheless provides important insights for students of security. This chapter engages postcolonial thought on security issues by focussing on two key moments in its development and the work of key postcolonial thinkers. It highlights both shared assumptions and important differences between proponents while stressing the myriad ways in which postcolonialism can enrich our understanding of security through its sensitivity to questions of colonial legacies, racism, and inequality.

In this chapter, students will learn about the debates concerning security within liberal thought. The first section outlines traditional/Kantian liberalism. The second section introduces liberal economic thought regarding peace and war—the ideas of ‘douce commerce’. The third section describes the democratic peace thesis and reviews the major discussions on the idea that liberal states do not fight wars with other liberal states. The fourth section outlines neoliberal institutionalism and its implications for thinking about security. The last section outlines how liberal thought deals with global transitions and the potential end of American hegemony.

In this chapter, students will learn about the concept of war and how it continues to evolve in line with the human societies that wage it. The chapter starts by examining different approaches to defining war and distinguishing it from several related activities before summarizing how most human societies developed the habit of warfare. The third section discusses how the character of contemporary warfare has changed with reference to debates about Revolutions in Military Affairs and so-called new and old wars. Finally, the chapter discusses how urban spaces, cyberspace, and outer space are becoming increasingly important domains for waging war.

In this chapter, students will learn about the principal organs of the United Nations and their role in maintaining international peace and security, the world body’s primary mandate. It provides an overview of the UN system as well as a short history of its contributions to security studies. It also addresses key threats confronting the globe in the 21st century—such as terrorism, mass atrocities, and weapons of mass destruction—and assesses the UN’s capacity to meet these security challenges.

In this chapter, students will learn how cybersecurity has become a key issue in global security. Once the primary domain of military and intelligence activities, cyber attacks and intrusions have had a broad impact, from the attacks against Georgia and Estonia to Stuxnet to the recent disruptions to operational and information technology. Cyber capabilities are no longer solely the province of states. Nonstate actors, such as criminals, terrorists, and ‘hacktivists’ have adapted cyber power for their own purposes. Private businesses find themselves on the frontline of cyber conflict every day. Rapidly evolving computer technology is a considerable challenge to standard strategies of conflict and deterrence as well as to the creation of norms.

Why did modern terrorism arise as a form of political violence? Scholars have located its origins in the mid-nineteenth century, a development that culminated in a global wave of terrorism and contributed to the outbreak of World War I. Despite consensus on its period of origin, we lack any explanation for why this development occurred. This article forwards a social theory for the origins of modern terrorism. Civic associations, which proliferated globally in the nineteenth century, provided the opportunity and motivation for the development of terrorism. Associations not only fostered the social and human capital necessary for terrorism; they also frequently generated grievances through an inability to enact political change and via ideological propaganda. I test this theory using an original global dataset of terrorist groups formed between 1860 and 1945. Statistical analysis reveals that cities with a YMCA, an exogenous indicator of associationism, were much more likely than those without to see the formation of terrorist groups. Additionally, terrorist groups are formed during civil wars, indicating that armed conflict can spur dramatic innovations in violent contention.

Contrary to popular perceptions, United Nations (UN) peacekeepers engage in combat fairly frequently. A central challenge facing the UN is thus calibration between force and politics: ensuring the organization’s combat power is harnessed to viable political strategies for peace. However, the epistemic community on peacekeeping remains deeply divided between skeptics and proponents of “robust” operations, where peacekeepers are expected to use force to implement mission mandates. This article suggests that militarily effective, robust peacekeeping is most important for improving civilian protection and ensuring mission credibility in theaters where there is no peace to keep; proposes a novel framework and typology to assess combat effectiveness in UN peace operations; and compiles descriptive statistics for the 1948–2020 period. Finally, case studies of four battles involving UN peacekeepers in the Democratic Republic of the Congo illuminate the conditions that are conducive to the UN’s combat effectiveness.