Course description
Justifying war and securing peace have been major subjects for legal thought and practical regulation since the beginning of recorded history. For most of this vast period, and in most civilizations, the conceptualization and organization of restoring and ensuring peace have been premised on the legal conception of war. As long as war was considered, as it has been for over two millennia in the European tradition, as an instrument for the pursuance of rights, peace could not be construed as legally unbreakable. This approach to war also informed the rules on waging war, which dictate the behavior of belligerents and the level of protection of both combatants and non-combatants during war. As such, concerns about humanity have generally taken second place, not only in practice but also in the theoretical construction of the law, throughout the ages.
The 20th century has been marked by a veritable revolution in international law with regard to the laws of war- and peacemaking. Between the Covenant of the League of Nations and the Charter of the United Nations, the right to war was first restricted and then overturned by a general prohibition for states to resort to war or to lesser forms of use of force. This revolution was largely concomitant to the rise of humanitarian concerns, which led to the emergence of international humanitarian law. While this was meant to constitute a radical break with the past, both in state practice and legal doctrine, old traditions, ideas, and doctrines persist. This has thrown the law about war and peace, arguably the most significant part of the politico-legal constitution of the world in disarray. The uncertainty has been exacerbated by the rise of internal armed conflicts and the ‘War on Terror’, leaving the institutions and proponents of a world order and international law badly armed to provide peace and security today. In this context, concerns about international humanitarian law and human rights law have sometimes become double-edged, in that more human forms of warfare serve as platforms to argue for the perpetuity of limited forms of ‘warfare’.
This course introduces students to one of the core historical subjects of the normative regulation and organization of international order. It discusses the historical development of the laws and institutions for making war and peace from Antiquity to the present war in Ukraine. It integrates theoretical reflections by legal and political thinkers with the practices of rulers, governments, and diplomats for the justification of war and the making of peace.
The course covers the Ancient Near East, classical Greece and Rome before moving to the Christian and Islamic world in the Middle Ages. The course gives ample attention to the crucial developments in the Early Modern Age, both with regard to the development of the sovereign state and European colonization and empire-building outside Europa. It then turns to modern international law and imperialism in the nineteenth century. The Covenant and Charter eras are discussed in depth. The course ends with several recent case studies.

Bibliography and syllabus

All texts are made available on Moodle.

Week 1: Introduction to the ‘laws of war and peace’ and early beginnings
Stephen Neff, War and the Law of Nations. A General History (Cambridge UP 2005) 13-38.
Week 2: The Roman legacy
Randall Lesaffer, ‘Chapter 3: The Greek and Roman World (600 BCE-650 CE)’, in Idem (ed.), Sources to the History of International Law in Europe and the West (in preparation), only section 2: The Roman conceptions of international law.
Week 3: The medieval just war doctrine
Stephen Neff, War and the Law of Nations. A General History (Cambridge UP 2005) 45-76
Randall Lesaffer, ‘Aggression before Versailles’, European Journal of International Law, 29 (2018) 773-808, 773-777.
Randall Lesaffer, ‘Chapter 5: Late-medieval Europe (1000-1453)’, in Idem (ed.), Sources to the History of International Law in Europe and the West (in preparation), only introductions to sections 1 and 2.
Week 4: The crusades and the Spanish conquests in America
Randall Lesaffer, ‘Chapter 5: Late-medieval Europe (1000-1453)’, in Idem (ed.), Sources to the History of International Law in Europe and the West (in preparation), entire section 3.
Week 5: The classical law of nations (1500-1800)
Randall Lesaffer, ‘The law of nations in Renaissance Europe’ in Randall Lesaffer (ed.), The Cambridge History of International Law, vol. 6: International Law in Early Modern Europe, Cambridge: Cambridge University Press 2025, 3-57.
Randall Lesaffer, ‘The law of nations in Old Regime Europe’ in Randall Lesaffer (ed.), The Cambridge History of International Law, vol. 6: International Law in Early Modern Europe, Cambridge: Cambridge University Press 2025, 381-420.
Week 6: Just and legal war under the classical law of nations
Randall Lesaffer, ‘The laws of war- and peace-making’ in Randall Lesaffer and Janne E. Nijman (eds.), The Cambridge Companion to Hugo Grotius (Cambridge: Cambridge University Press 2021) 433-56.
Week 7: Peacemaking in early modern Europe
Randall Lesaffer, ‘Peacemaking in Renaissance Europe’ in Randall Lesaffer (ed.), The Cambridge History of International Law, vol. 6: International Law in Early Modern Europe, Cambridge: Cambridge University Press 2025, 232-62.
Randall Lesaffer, ‘Peacemaking in Old Regime Europe’ in Randall Lesaffer (ed.), The Cambridge History of International Law, vol. 6: International Law in Early Modern Europe, Cambridge: Cambridge University Press 2025, 581-619.
Week 8: Aggression under the classical law of nations
Randall Lesaffer, ‘Aggression before Versailles’, European Journal of International Law, 29 (2018) 773-808, 777-789.
‘War and the use of force in Old Regime Europe’ in Randall Lesaffer (ed.), The Cambridge History of International Law, vol. 6: International Law in Early Modern Europe, Cambridge: Cambridge University Press 2025, 495-516.
Week 9: A century of anarchy (1815-1918)?
Stephen Neff, War and the Law of Nations. A General History (Cambridge UP 2005) 215-49.
Randall Lesaffer, ‘Aggression before Versailles’, European Journal of International Law, 29 (2018) 773-808, 789-798.
Week 10: Towards the jus contra bellum (1899-1940)
Stephen Neff, War and the Law of Nations. A General History (Cambridge UP 2005) 285-313.
Randall Lesaffer, ‘Aggression before Versailles’, European Journal of International Law, 29 (2018) 773-808, 789-808.
‘Randall Lesaffer, Peace through Law: the Hague Peace Conferences and the rise of the ius contra bellum’, in Maartje Abbenhuis, Christopher Ernest Barber and Annalise R. Higgins (eds.), War, Peace and International Order? The Legacies of the Hague Conferences of 1899 and 1907, Routledge Studies in Modern History; London and New York: Routledge 2017, 31-51.
Week 11: The Charter Era (1945-present): general use of force law and its development
Stephen Neff, War and the Law of Nations. A General History (Cambridge UP 2005) pp. 314-56.
Week 12: The Charter Era (1945-present): recent cases
Randall Lesaffer, draft chapter from A New World Order? Peace, War and International Law at the End of History (forthcoming).

Learning outcomes of the course
At the end of the course, students have
- A general understanding of the historical development of major doctrines and institutions about the justification of war, the waging of war, and the making of peace.
- An understanding of the current international law and order on these subjects.
- An insight into the place of legal norms and institutions in geopolitical decision-making about war and peace.
- An insight into the current security challenges for the global order that partially arise from the disorganization of the international legal system.

Teaching and evaluation method
Students are expected to read the literature for the week in advance of class and to take note of the subjects they want to see discussed with more depth in class. The lectures make ample use of historical texts, projected on screen, which are analyzed to discover and unearth the most salient points.

The evaluation consists of three parts:
- Student participation (activity and relevance): 10 % before midterm, 10 % after midterm
- Paper (app. 4.000 words): students choose a war or a peace treaty and analyze it with regard to the normative framework applied in their source. Students give a brief ten-minute presentation of the key findings of their paper, followed by a class discussion (40 % of the grade, divided 30/10). Students turn in their papers by 3 May.
- Open-book, written exam with 2 essay questions (40 % of the grade). Students receive 4 questions and can choose any 2 to answer.

Last updated: January 21, 2026