The Ethics of War

The document provides a historical overview of Western philosophical approaches to war. It details the transition from ancient 'realist' and 'pacific' orientations to the medieval systematization of Just War Theory by figures like Augustine and Aquinas. It further examines the 'Perpetual Peace Theory' developed by Hobbes, Rousseau, and Kant, which sought structural institutional solutions to conflict. Finally, it notes the late 20th-century revival of Just War Theory, sparked by the Vietnam War and the work of Michael Walzer, leading to modern discussions on humanitarian intervention and 'jus post bellum'.

• Ancient Western philosophy was divided between an 'agonistic conception'—where war was seen as a primordial reality and a force for maintaining order—and a 'pacific orientation' that viewed peace as the normative reality, requiring any resort to war to be justified.
• The Just War tradition was systematized in the medieval period, notably by Thomas Aquinas, who established three core requirements for a war to be considered just: legitimate authority, just cause, and right intention.
• A critical distinction in classical just war literature (13th to 17th centuries) was made between defensive war, which could be initiated by lower officials or individuals in cases of necessity and imminence, and offensive war, which was the exclusive prerogative of the supreme authority (the prince).
• Francisco de Vitoria introduced the concept of 'rights of war' (jura belli), which shifted focus toward 'jus in bello' (conduct during war), though he largely viewed these as unilateral rights granted only to the just belligerent.
• Perpetual Peace Theory emerged as a structural approach to eradicating war, moving from Thomas Hobbes's analysis of the 'state of nature' and the social contract to Immanuel Kant's proposal for a global pacific federation.
• Immanuel Kant argued that the spread of constitutional republics and global economic integration (trade) would naturally promote peace, as democratic decision-makers bear the costs of war and commerce is incompatible with conflict.
• Just War Theory saw a significant revival in the late 20th century, driven by debates over the Vietnam War and the influence of Michael Walzer, leading to new inquiries into humanitarian intervention, non-combatant immunity, and 'jus post bellum' (justice after war).

APA

Peace Research Institute Oslo (n.d.). The Ethics of War. https://cdn.cloud.prio.org/files/6fae2b1e-78f1-4272-95c1-dcc7e37c2509/The Ethics of War Part I Historical Trends.pdf?inline=true

Chicago

Peace Research Institute Oslo. The Ethics of War. n.d. https://cdn.cloud.prio.org/files/6fae2b1e-78f1-4272-95c1-dcc7e37c2509/The Ethics of War Part I Historical Trends.pdf?inline=true.

Wikipedia

{{cite report |author=Peace Research Institute Oslo |title=The Ethics of War |url=https://cdn.cloud.prio.org/files/6fae2b1e-78f1-4272-95c1-dcc7e37c2509/The Ethics of War Part I Historical Trends.pdf?inline=true |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{peaceresearchinstituteoslondethics, author = {{Peace Research Institute Oslo}}, title = {{The Ethics of War}}, institution = {Peace Research Institute Oslo}, url = {https://cdn.cloud.prio.org/files/6fae2b1e-78f1-4272-95c1-dcc7e37c2509/The Ethics of War Part I Historical Trends.pdf?inline=true}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }