This paper examines just war theory from its ancient and medieval philosophical origins through its application — or conspicuous absence — during the Hundred Years' War. Drawing on Augustine's foundational principles, Saint Thomas Aquinas's formal criteria, and modern ethical frameworks, the paper traces how civilizations have attempted to impose moral boundaries on warfare. It then turns to the medieval European context, explaining why feudal politics made just war concepts largely irrelevant during the reigns of Henry IV, V, and VI. Finally, the paper analyzes Shakespeare's Henry V as an indirect meditation on honorable leadership and the personal character traits that parallel the ethical ideals embedded in just war theory.
The idea of a "just war" is a genuine conundrum. How can one group of people consider it "right" or "just" to apply military force against another group? When can actions that create devastation, economic hardship, and the deaths of thousands be considered morally acceptable? In a civilized society, the concept of a just war has become the centerpiece of many discussions and has served as a restraint on the hawkish tendencies of nations that pride themselves on freedom and individual liberty. In order for a nation to engage in an activity that causes harm to another group, there must be a justifiable reason.
Just war theory deals with the justification of how and why wars are fought. Often the justification is rooted in either theoretical ethical arguments or in long-standing historical hostilities between peoples. The theoretical aspect is concerned with ethically justifying the engagement of war as well as the forms warfare takes. The historical aspect — sometimes called the "just war tradition" — addresses the accumulated body of rules and mutual agreements that have governed various wars across the ages. International conventions such as those established at Geneva and The Hague are collections of historical rules aimed at limiting certain kinds of warfare. The Geneva Convention addressed how prisoners are to be treated and how military campaigns are to be directed toward military assets rather than civilian targets. Ethics play a tempering role in these standards, staking out a middle ground by which nations can wage war while still demonstrating respect for the human rights of others.
Historically, just war norms have typically evolved between similar enemies. When enemies differ greatly in religious beliefs, race, or language, war conventions have rarely been applied because the parties share no common ground on which to base mutual understanding. Nonetheless, modern philosophers have contested the selective application of these boundaries. If just war theory is founded on a universal concern for the well-being of all peoples, then the rules of war should apply equally to all — that is, just war theory should be universal (Mosely, Internet Encyclopedia of Philosophy).
In some respects, the just war concept is as old as warfare itself. Early records of individual warriors include ideas of honor in the way soldiers treated their captives and conquered peoples. Even cultural depictions of gunslingers in the American West invoked codes of honor: a gunfighter would never "shoot someone in the back," demonstrating a code of conduct within the process of personal dispute. While the specifics of what is honorable differ across peoples, times, and places, the persistence of this argument demonstrates that human beings have long been concerned with the justice of their actions when they pick up a weapon or command a force with the purpose of delivering deadly force against another individual or group.
The idea of a just war has been discussed as far back as biblical times. When the children of Israel completed their exodus from Egypt and were about to enter the land they believed was their divine right, they were commanded to war against the existing peoples and take the land for themselves (Holy Bible, Joshua, chapter 1). Moving into the early centuries of the Common Era, Augustine was among the first to confront the conundrum of justifying war when those waging it had declared their allegiance to Christianity. Living in Rome after Constantine's Edict of Milan declared the empire Christian, Augustine faced the pressing problem of justifying Rome's ongoing military conquests. He was among the first to clearly articulate a basis for measuring the justice of a war. The worthy causes he identified include: preservation of the well-being of the state; punishment of neighboring nations that refused to make amends for wrongs committed by their subjects; restoration of what had been taken unjustly; and — given that he lived within the Roman Empire — the expansion of empire when land was being taken from a tyrant (City of God, Book 4, Para. 15).
Augustine saw wars as "stern and lasting necessities" even when they produced misery for human beings. War was simply part of the human condition — even good kings waged wars (Wells, 1996). These ideas continued to evolve and were refined by Saint Thomas Aquinas, who was the first to clearly and specifically define the ethical basis for a just war. His work is still considered foundational to just war theory.
Aquinas's criteria for a just war remain among the most influential articulations of the concept. They include the following principles:
Just Cause (usually understood as defense against an attack): If a nation is attacked, it has the just right to strike back and defend itself.
Right Authority (established political authorities, not private citizens): War is just when it is undertaken by legitimate authority working in favor of the citizens it governs, rather than by private individuals acting on their own behalf.
Right Intention (not the love of cruelty or the lust for power): The motive for war is an important element in assessing its justice.
Good Outcome (the good resulting from the war must outweigh the evil done by violence): Many people today question, for example, the justice of American aircraft dropping atomic bombs on Japan. The devastation to both military and civilian targets was horrendous. However, this single act ended a war that would have cost hundreds of thousands of lives on both sides had American forces been forced to land on the Japanese mainland.
Proportionality (do not use more force than necessary): This principle must be balanced against the legitimate desire to apply overwhelming force in order to achieve the military objective swiftly.
Reasonable Hope for Success (a reasonable chance that peace will result): If there is no hope of success, sending men into ongoing conflict is an immoral act.
"Consequentialist and intrinsicist objections to war ethics"
"Feudal politics and land disputes driving medieval conflict"
"Henry V as literary analogue for just war character"
In this way, one might stretch the concept of just war and argue that Shakespeare adhered to a similar code. Philosophers argued that wars conducted within humane boundaries — limiting devastation while still achieving their objectives — represented an honorable way to wage war. Shakespeare looked for a similar humility and clarity of purpose in the heart of a leader, and judged such a man worthy to be followed into battle. By contrast, the excessive, selfish, hedonistic, or unprepared antagonist was defeated. By analogy, armies that engage in war for selfish, vengeful, or barbaric purposes are like these failed leaders — and such dishonorable reasons for waging war ought not to be pursued.
This extended philosophical reading does hold a genuine value. Honorable actions, honorable motives, and honorable people look out for the welfare of others and seek to promote peace rather than to amass power for themselves. The unfortunate reality of our world, however, is that unjust and tyrannical motives can draw a just and moral people into armed conflict against their will — a truth as relevant today as it was in the age of Augustine, Aquinas, or Henry V.
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