This chapter provides a detailed genealogy of the development crimes against humanity, from its nineteenth century natural law origins through its codification in the Rome Statute, and finally its possible recodification in a new treaty. It subsequently traces the interpretative approaches of states towards the current draft proposal about a specialized treaty, ultimately concluding that states’ attitudes may fall into one of three categories – unity, evolution, or diversity. Unity refers to states who advocate for the new treaty to be a horizontal add on to the Rome Statute, making the two instruments consistent as a matter of text and application. Evolution, refers to states who advocate for the progressive interpretation of existing provisions, with a view to adjusting the definition of crimes against humanity consistently with new development, or expanding the list of crimes that fall in this category. Diversity, finally, refers to the possibility of states to continue developing the law even after codification, through evolutions in customary law or diversity in national codification.

This chapter deals with individual criminal responsibility rather than state responsibility. A range of international criminal courts and tribunals are examined, from the Nuremberg Tribunal following the Second World War to the more recent International Criminal Tribunal for the Former Yugoslavia, the International Criminal Tribunal for Rwanda and the Mechanism for International Criminal Tribunals, which deals with matters remaining after the demise of these tribunals. The International Criminal Court is discussed in some detail and in terms of governing principles and organisation, with references to relevant case law. A number of hybrid courts and other internationalised domestic courts and tribunals are then referred to, including those concerning Sierra Leone, Cambodia, Kosovo, East Timor and Bosnia. The chapter proceeds to examine a series of international crimes, from genocide to war crimes, crimes against humanity and aggression. These crimes are analysed and discussed in the light of practice and case law, both in terms of definition and implementation.

Arendt believed that “the idea of humanity” requires all nations to assume responsibility for major crimes of international, rather than purely domestic, concern. Her ideas about international criminal law grew from the Eichmann trial; they appear in Eichmann in Jerusalem and her correspondence with Karl Jaspers about the trial. This chapter provides essential background for her ideas by explaining the “lawyers’ law” concerning state sovereignty, sovereign immunity, crimes against humanity, and genocide. Arendt partly presupposes this background, but she also breaks with it in significant ways. Notably, Arendt breaks from the state-centered orthodoxy when she argues that its concepts don’t apply when a state itself becomes criminal. She also gives the term “crimes against humanity” a substantive meaning (crimes of international concern), which in her view includes genocide as a crime against humanity. In the lawyers’ law, these are distinct crimes with different definitions. The chapter explains what motives the lawyers’ law, to better understand Arendt’s alternatives.

International criminal law is the branch of public international law under which individuals may be held criminally responsible for the offences of genocide, crimes against humanity, war crimes, and the crime of aggression. International criminal law seeks to prevent impunity by holding accountable those individuals who are responsible for serious violations of international criminal law. This chapter begins with the history of international criminal law, starting with the aftermath of the First and Second World Wars, and ending with the creation of a spate of international criminal courts and tribunals in recent decades. The chapter then covers substantive aspects of international criminal law, namely the crime of genocide, crimes against humanity, war crimes, and the crime of aggression. Finally, the chapter covers key procedural aspects of international criminal law, including the jurisdiction of international courts and tribunals, the admissibility of cases, modes of liability, and immunities. The International Criminal Court is a focal point in this chapter

Genocide is a contested concept with normative, legal, political, and empirical dimensions, each pulling in different directions. The chapter emphasizes that, in addition, a fundamental contradiction exists in the concept: The legal definition, anchored in an international treaty, dominates the social sciences, even though the legal definition is problematic for the specification of a particular type of violence. The concept is thus perpetually trapped between legal and empirical imperatives, rendering it unwieldy for the social science objective of isolating a particular type of phenomenon. The chapter rejects the solution of jettisoning the concept, instead proposing a set of solutions for how to retain the concept and separate it from its legal origins. The chapter concludes by arguing that such solutions are unlikely to carry the day, but that social scientists should still seek to develop a rigorous conceptualization of the term that allows for the identification of specific types of political violence. Finally, a postscript offers an interim assessment – from the perspective of this chapter – of the war in the Middle East that began on October 7, 2023.

A framing case study describes the trial of Hissène Habré, the deposed leader of Chad who was prosecuted for multiple international crimes in Senegal. The chapter then discusses international criminal law. The chapter first discusses major principles of international criminal law and its evolution. It next discusses the key elements for establishing criminal guilt, including: the definition of core crimes; modes of responsibility and liability; and possible defences. Finally, the chapter surveys the major institutions that enforce international criminal law by discussing the operations of the International Criminal Court and the assertion of universal jurisdiction by domestic courts.

This chapter argues that Soviet crimes at times of war were both widespread and complex in their origin, goals, logic, and trajectory. It distinguishes and explains several forms of Soviet criminality during its defensive war against Germany in 1941–1945: crimes against humanity and war crimes, both perpetrated by agents of the state and often in accordance with explicitly formulated state policy; troop crimes, not guided by state policy but often understood to be in its fulfilment by the perpetrators; and a variety of violent and criminal behaviour emanating from small group bonding, both within the military and outside of it. The chapter explains their origins and charts the reasons why there was so much silence about the criminality of the Soviet war effort after victory.

In armed conflicts, when people massively go missing, enforced disappearance is prohibited both by the ICPPED and customary international humanitarian law (IHL). While IHL is the primary regulator in armed conflicts, ICPPED complements and reinforces IHL protection from enforced disappearance including by providing more direct legal basis for the State Parties then customary nature of the matching IHL provisions which are often elusive for national practitioners. Obligation under ICPPED to introduce enforced disappearance as an autonomous and continuous domestic crime should provide potentially strong accountability mechanism given the absence of enforced disappearance from underlying offences considered war crimes and the contextual limitations of enforced disappearance as a crime against humanity and may also help break the silence about the disappeared. Limitation of the ICPPED’s definition of enforced disappearance as state-sponsored crime may be overcome in armed conflicts by the commensurate IHL prohibition which applies to non-state actors too.

Chapter 3 is a close reading of several documents and transcripts of the Case of Duch of the Cambodia Tribunal. Interestingly, notions of humanity and inhumanity were used by several parties: prosecutors, attorneys for civil parties but also the defendant’s lawyer and Duch himself declared that the latter was dehumanised. In a second move, these findings will be put in a philosophical context by bringing them in conversation with the work of Hannah Arendt, thus showing the structure of dehumanisation and rehumanisation.

The loss of human life and physical injuries through violence are an inherent consequence of armed conflict, including civil wars. Deliberate atrocities – such as war crimes, crimes against humanity, genocide, politicide and “ethnic cleansing” – have been a conspicuous feature of many wars. Civil wars – whether correctly or incorrectly from an empirical perspective – have often been regarded as particularly vicious, transgressing all norms of decency in the frequency and type of atrocities. This chapter explores several key questions that have arisen in the conflict analysis field in relation to atrocities in civil war – and war generally. Are atrocities specifically associated with certain “types” of civil war, such as separatist, ideological, intercommunal, or resource conflict? Are there patterns in terms of which types of actors – state or non-state rebel groups – are more likely to perpetrate atrocities? What motivates individuals and groups to perpetrate atrocities, and what “role,” if any, do such atrocities play in armed conflict? Do atrocities play a strategic role, or are they better understood as a manifestation of individual and group sadism, revenge, and hate or fear, spread in the contemporary era by social media? Are all combatants capable of perpetuating atrocities in the “right” circumstances? The chapter concludes with a discussion of the international norms that have emerged over the last century – which prohibit war crimes, crimes against humanity, and genocide – and the calls for accountability and justice after mass atrocities that have arguably made a significant although limited impact on conduct in war. As a part of this, “transitional justice” has emerged as an important topic, designed to address the societal impact and legacy of atrocities.

A hybrid legal discipline dealing with the relationships between the right to punish and state sovereignty, international criminal law (ICL) overturns classical conceptions of the state, law and justice. Its existence, foundations, scope and effectiveness are determined by the outcome of an attempt – which has proved more or less successful throughout the different phases of its evolution – to reconcile it with the founding principles of the modern state, sovereignty and legality, inherited from the Enlightenment. Adopting a historical perspective helps us its development, on either side of the pivotal moment represented by the creation of the League of Nations: the starting point marked by the 1919 Paris Conference and the immediate aftermath of the First World War; and the turning point marked by the work of the League and international legal doctrine in the interwar era. These two crucial phases saw a string of initiatives which, rather than failures, can be interpreted as a series of necessary transformations for the emergence of a new discipline and, more generally, a profound change in the global legal and judicial order.

This chapter explores the interaction between international human rights law (IHRL) and international humanitarian law (IHL), as well as international criminal law. It examines how IHRL influences the application and development of IHL and how human rights principles are integrated into international criminal procedures and substantive law. The chapter discusses the mutual reinforcement and potential conflicts between these branches of international law, highlighting the need for a coherent and integrated approach. It also explores the role of international courts and tribunals in applying and interpreting IHRL, IHL, and international criminal law, and the challenges in ensuring compliance and accountability.

Atrocity crimes and grand corruption: the chapter argues that adopting a “corruption lens” is useful to characterize and understand patterns of crimes against humanity, especially whether acts are widespread or systematic, whether there is a state or organizational policy, how high-ranking actors are tied to crimes by subordinates (“modes of liability”) and whether specific acts constitute crimes under the ICC’s Rome Statute. The chapter uses examples from Mexico and Venezuela to illustrate.

Genocide is sometimes called the ’crime of crimes’. The word was coined by Raphael Lemkin in 1944, then declared an international crime by the United Nations General Assembly. In 1948, the Genocide Convention was adopted. As the first human rights treaty of modern times, it constituted a significant intrusion into what had previously been a matter exclusively of domestic concern. This explains the narrow definition of the crime of genocide. It requires proof of an intent to destroy a national, ethnic, racial or religious group. Only a half century after its adoption did the Genocide Convention take on real significance with inter-State cases being filed at the International Court of Justice and many prosecutions at the International Criminal Tribunals for the former Yugoslavia and Rwanda. The Convention requires that States Parties punish genocide but they are also required to prevent it, even when it takes place outside their own territory. More than 150 States have ratified the Genocide Convention. Genocide is also prohibited under customary international law. It is generally agreed that the duty to punish genocide is a peremptory norm of international law (jus cogens).

The post-First World War minorities treaties regime was an initial attempt by international law to address the rights of national and ethnic minorities. Its shorcomings prompted Raphael Lemkin, in his book Axis Rule in Occupied Europe, to propose a new category of international crime that he named genocide. The International Military Tribunal prosecuted acts of genocide using the category of crimes against humanity. Several of the defendants were convicted of acts aimed at destruction of Europe’s Jewish population. However, crimes against humanity were confined to acts associated with aggressive war. At the first session of the United Nations General Assembly in 1946, a resolution on genocide was proposed in order to address the peacetime atrocities that were neglected in the Nuremberg judgment. The resolution recognized genocide as an international crime and called for preparation of a convention.

Acts of cultural genocide were deliberately excluded by the drafters of the Genocide Convention, although this was very controversial. The term ’cultural genocide’ is widely used and is not incorrect but it is not contemplated by the Genocide Convention. The line between cultural genocide and physical genocide is blurred in the case of ethnic cleansing, which does not necessarily involve the physical destruction of the group. The use of nuclear weapons may constitute an act of genocide.