Editing Just war theory (section)

====Saint Thomas Aquinas====
{{See|Thomas Aquinas#Just war}}
[[File:Saint Thomas Aquinas Reading.png|thumb|[[Thomas Aquinas|Saint Thomas Aquinas]] contributed to the development of the just war theory in medieval Europe. ]]
The just war theory by [[Thomas Aquinas]] has had a lasting impact on later generations of thinkers and was part of an emerging consensus in [[medieval Europe]] on just war.<ref name=":1">{{Cite book|title=Thomas Aquinas on War and Peace|author=Gregory M. Reichberg|publisher=Cambridge University Press|year=2017|isbn=9781107019904|page=viii}}</ref> In the 13th century Aquinas reflected in detail on peace and war. Aquinas was a [[Dominican friar]] and contemplated the teachings of the Bible on peace and war in combination with ideas from [[Aristotle]], [[Plato]], [[Socrates]], [[Saint Augustine]] and other philosophers whose writings are part of the [[Western canon]]. Aquinas' views on war drew heavily on the {{lang|la|[[Decretum Gratiani]]}}, a book the Italian monk Gratian had compiled with passages from the Bible. After its publication in the 12th century, the {{lang|la|Decretum Gratiani}} had been republished with commentary from [[Pope Innocent IV]] and the Dominican friar [[Raymond of Penafort]]. Other significant influences on Aquinas just war theory were [[Alexander of Hales]] and [[Henry of Segusio]].<ref>{{Cite book|title=Thomas Aquinas on War and Peace|author=Gregory M. Reichberg|publisher=Cambridge University Press|year=2017|isbn=9781107019904|page=vii}}</ref>

In ''[[Summa Theologica]]'' Aquinas asserted that it is not always a [[sin]] to wage war, and he set out criteria for a just war. According to Aquinas, three requirements must be met. Firstly, the war must be waged upon the command of a rightful [[sovereign]]. Secondly, the war needs to be waged for just cause, on account of some wrong the attacked have committed. Thirdly, warriors must have the right intent, namely to promote good and to avoid evil.<ref>{{Cite book |last=Aquinas |first=Thomas |url=https://ccel.org/ccel/aquinas/summa/summa |title=Summa Theologica |publisher=Christian Classics Ethereal Library |pages=pt. II, sec. 2, q. 40, a. 1}}</ref><ref>{{Cite book|title=The Oxford Handbook of Ethics of War |editor=Seth Lazar |editor2=Helen Frowe|publisher=Oxford University Press|year=2018|isbn=9780199943418|page=114}}</ref> Aquinas came to the conclusion that a just war could be offensive and that injustice should not be tolerated so as to avoid war. Nevertheless, Aquinas argued that violence must only be used as a last resort. On the [[battlefield]], violence was only justified to the extent it was necessary. Soldiers needed to avoid cruelty and a just war was limited by the conduct of just combatants. Aquinas argued that it was only in the pursuit of justice, that the good intention of a moral act could justify negative consequences, including the killing of the innocent during a war.<ref>{{Cite book|title=The Oxford Handbook of Ethics of War |editor=Seth Lazar |editor2=Helen Frowe|publisher=Oxford University Press|year=2018|isbn=9780199943418|page=115}}</ref>