How did moral or legal thinking about war, especially "just war," evolve from ancient times through the Middle Ages? How does that relate to Walzer's book Just and Unjust Wars? (With Thucydides, Augustine, Aristotle, Cicero, and Aquinas)

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"Just war theory" can be found in various forms across the globe from ancient times to the present. It was first documented in Ancient Egypt. Contrary to popular thought that just war theory originated in Christian Europe, there is evidence that the idea was present globally prior to Christianity’s existence. The ideology is also highly present in Confucian philosophy in Ancient China. The Zhou dynasty developed a lot of thought on the ethics of war. Primarily, the belief was that war was to be a last resort and was only just if won. War could only be waged by sovereign entities. India had its own philosophies on war and justice. Hinduism has its own version of just war theory as well. The iconic Indian epic Mahabharata, written in 400 BCE, provides some of the first text about just war theory. It argues that war must be between equal adversaries, it must use fair weaponry, it must treat all soldiers with dignity, and it must have a good reason.

Aristotle (born in 384 BCE) wrote of the uses of war. He argued that war could be used in self-defense to prevent becoming enslaved. However, in his argument, he also justifies the use of slaves as soldiers in war. Here he very controversially links one’s freedom to the enslavement of another.

Most written about is the Christian point of view. St. Augustine, who was born in the year 354, is the first Christian theologist documented as writing and/or talking on the concept of “just war.” He used the Bible to justify war as a way of ending sin. He wrote these beliefs in Contra Faustum Manichaeum. In his next book, City of God, St. Augustine coins the phrase "just war." He says,

But, say they, the wise man will wage Just Wars. As if he would not all the rather lament the necessity of just wars, if he remembers that he is a man; for if they were not just he would not wage them, and would therefore be delivered from all wars.

Much of St. Augustine’s writing quotes Cicero. He argues for a model state which uses war justly to govern. He believed that if justice was not practiced by a sovereign state, a more just government could intervene using war.

The next Christian theologist documented is St. Thomas Aquinas who was born in the year 1225. He modified St. Augustine’s theory by suggesting that there were criteria for a war to be “just.”

  1. The war needed to be started by a sovereign authority.
  2. The war needed to have a “just” cause.
  3. The war needed to have good intentions.

In his writing, the Summa Theologica, he wrote about how philosophy and religion are two distinct but highly intertwined bodies of thought.

The School of Salamanca, made up of Spanish and Portuguese theologists, started in the 1400s. It argued the evils of war, suggesting that war should only be used to stop a worser evil. They provided the following criteria for a “just war”:

  1. A war needs to be in self-defense.
  2. A war can be used to prevent further bloodshed.
  3. A war can be used as a form of punishment.

The Catholic Church provides the Just War Doctrine in the Catechism of the Catholic Church.

  1. A war must have a damaging effect.
  2. Countries must have exhausted all diplomatic possibilities.
  3. It must be possible for the country to win.
  4. The evils of war must not outweigh the evil trying to be conquered.

There are three agreed-upon Laws of War that are recognized by most nations. Jus ad bellum are the laws that govern when it is ethical to start a war. Jus in bello are the laws that explain how a war should be ethically conducted. Finally, jus post bellum explains how and when a war can be ethically ended.

Walzer in Just and Unjust Wars argues that the primary component of just war theory is self-defense. He also believes that war is just when used to stop genocide; however, he makes a clear distinction that it must be used to end the massacre, not punish the government. He opposed the Vietnam War and the War in Iraq.

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