Philosophy of War: A Brief Analysis on Principles and Justifications (Section 1)


This is the first section of a three-part analysis. It draws on theories from three theorists, Carl von Clausewitz, Sun-tzu, and Thomas Aquinas, for insights into theories on war and justification for waging war. Although Thomas Aquinas is known more for his contributions to theology and philosophy, he was included in this project because his ideas pertaining to “just war’ has a semblance of theory. The theoretical and philosophical contributions developed by these three patriarchs are used to evaluate specifically chosen wars across the historical spectrum they include: The Peloponnesian War, the World Wars, and the Soviet-Afghan War. A historiography of the literature for each war is provided followed by an evaluation through the lens of the three theorists. Primary sources were used to extract information regarding the chosen wars they include: Thucydides, John Keynes, Treaty of Versailles Document, State Department Bureau of Public Affairs, The Russian General Staff, and the memoirs of Vladislav Tamarov—Afghanistan a Russian Soldiers’ Story. The primary sources extracted from the theories come from the patriarchs’ own publications they include: On War, by Clausewitz; Summa Theologica, by Thomas Aquinas; and The Art of War, contributed to Sun-tzu. The thesis is: The theories pertaining to war developed by Clausewitz, Sun-tzu, and Aquinas are not constrained by time periods, they are applicable to the past, present, and future. The properties from which the theories persist have always existed in humanity, but it took certain mind(s) to extrapolate through observations their place among civilizations as they evolved and clashed.


The act of war has produced horrific conditions for civilizations while at the same time it has created the possibility of liberation for those bound by forced inhumane suffering brought on by their oppressors. Clausewitz, one of the greatest theorists to write about war argued that no sensible man starts a war, or at least, he should not do so, without having a clear vision as to what he intends to achieve and how he intends to conduct it.[1] Sun-tzu, if he ever actually existed, also wrote theories on war or at least these ancient theories we have are credited to this historical actor. Nonetheless, Sun-tzu and Clausewitz’s theories are studied by military institutions all over the world. According to Clausewitz, “War therefore is an act of violence intended to compel our opponent to fulfill our will.”[2] Society has an understanding of what defines war. However, the conditions in which a society is justified for initiating war is less agreeable. Thomas Aquinas developed a justification for waging war that he extracted from the Greek philosopher Aristotle, Christian theology, and Scripture. It can be summed-up by focusing on three things: First, war does not belong to the private citizen therefore only rulers charged with protecting the commonwealth have the moral authority to initiate war by calling upon the state’s citizens. Second, the enemy must deserve to have war waged on them because of some act of evil they have inflicted (just cause). Third, the rulers who wage war must have the right intentions—to promote good while suppressing evil, never for the purpose of gain but to preserve righteousness.[3] This study will analyze the theoretical and philosophical contributions developed by those who have profoundly influenced theories pertaining to war and how it should be conducted. It will be approached through the evaluation of specified wars across the historical spectrum disclosing insights into the theories that guide strategists who participate in this aberration. 

The Peloponnesian War

Athens’ rise to dominance in the fifth century was primarily attributed to their Navy. They controlled most of the Mediterranean through approximation to location, that is, out of the 179 states the most remote was within a 200-250 mile range from Athens (eight-day voyage by sea). Still, they did not go unchallenged. The militarized polis (πόλις) city-state of Sparta organized the Peloponnesian League to engage in a series of land and sea conflicts known as the Peloponnesian War. Athens became overextended as the skirmishes prolonged. Athens’ empire weakened as they lost land after a series of defeats, and in 445 BC they were forced to negotiated a peace. In 446, Athens and Sparta agreed on a Thirty Years Peace arrangement. This resulted in two great powers in the ancient world that would remain suspicious of each other until the Second Peloponnesian War broke out in 431.[4]

Sparta was unique, they had conquered their neighbors, the helots, and subjected them to the forceful service of the state, a form of serfdom. The helots provided food for the Spartans by farming the land. This liberated the Spartans from mundane tedious labor enabling them to engage in continuous military training from age seven and serving until age sixty when military service was no longer a requirement. The alliances Sparta formed with surrounding city-states required them to serve under Spartan command when needed, swearing allegiance to have the same friends and enemies as Spartan in return for the great power’s protection.[5] Spartan’s style of government was complex; it contained elements of monarchic, oligarchic, and democratic. An elected council of men over sixty chosen from privileged families represented the oligarchic element, an assembly of men over the age of thirty represented the democratic element, and two kings that served for life represented the monarchic element.[6]

Athens had a unique history as well. Athens emerged as the world’s first democratic style government in the fifth century. Democracy, for Athens, depended on its maritime empire. During the Persian war Athenian allies of the Greek city-states invited Athens to take the initiative in the fight for liberation against the Persians. Nearly all members of the Athenian alliance ceased maritime operations electing to pay into a centralized treasury associated with the alliance which would fund Athens’ Navy and maritime operations. This resulted in the largest and best Naval force the world had known. The powerful Athenian Navy provided protection for their merchant ships beyond the Mediterranean.[7] After the Persian War Athens rebuilt their walls around the city and their large empire became concerning for the Spartans. In fact, Spartan protested Athenian’s desire to rebuild their walls. However, the walls went up with no regard for the Spartan’s opposition. Embittered, and resentful of Athens’ powerful empire the Spartans made no additional complaints.[8]

Belligerent Allies and Fear

One of the many problems with weaker sovereign allies is the possibility of them dragging their greater much more capable ally into a major conflict with an opposing great power. This scenario materialized for the Spartans when one of their allies, Corinth, became embroiled in a dispute with Corcyra. The Corcyraeans’ Navy was second only to Athens’. However, the Corcyraeans feared that the Corinthians would enlist the help of other alliances within the Spartan league. The Corcyraeans were neutral and did not have an alliance with either of the two great opposing powers, Sparta and Athens. Thus, once the Corcyraeans realized that the Corinthians were determined to wage war, the Corcyraeans sought the help of the Athenians. The provisions of the Thirty Years Peace treaty, ratified in 446-45, allowed for neutral powers to join the alliances of either of the two great powers. So, Athens would have been within the confines of the treaty to accept the Corcyraeans’ request for assistance. Moreover, the Corcyraeans appealed to Athens’ fears, arguing that if they succumb to the Corinthians their fleet would fall into the control of the Spartan league.[9] This would present a major challenge to Athenian maritime power in the region, tipping the balance of power in Spartans’ favor. Still, caution was needed to avoid unintendedly setting off a premature war with the Spartans.

Historian Donald Kagan provides a detailed account of the events that led to the Peloponnesian War in his book, On the Origins of War. Kagan delivers a superb narrative of the tactics used by Corinth and the Corcyraeans to persuade the two great powers to choose a side.  This account will be brief and condensed because understanding the psychology of the ancients are problematic. It becomes more problematic when modern researchers attempt to understand motivations that extend beyond what has been recorded by those closest to the event or to speculate on surviving artifacts forcing them to fit a supportive testimony. The focus will be on what occurred and how those actions fit into a general theory of war and justifications developed by one or more of the three patriarchs introduced at the beginning of this study.

After some debate, primarily rhetoric, embellishment, and hyperbole the two belligerent city-states had stirred the fears of both the Spartans and Athenians. As previously stated, Athens was cautious. They decided to send only ten warships to the area, rather than a large armada, presumably this would be less likely to provoke Sparta. Essentially, the Athenians made an alliance with the Corcyraeans that was defensive only. The Greek general Pericles was most likely behind this idea. There are two primary sources used for this interpretation, Plutarch and Thucydides. Kagan explores this in On the Origins of War, but he argues against Thucydides’ claim that the Athenians voted for the treaty with Corcyra because they viewed a war with Sparta as inevitable (Kagan argues against Thucydides’ interpretation in his earlier publication The Outbreak of the Peloponnesian War).[10] Nevertheless, Corinth initiated war with Corcyra assuming the Athenians would stand aside. With the help of a few colonies and allies the Corinthians attacked the Corcyraeans’ fleet in September of 433.[11]

The Corcyraeans had 110 warships and the Corinthians, combined with their allies, had 150 warships. It wasn’t long before the Corinthians gained the advantage and began to press the Corcyraeans. The Athenians realized they could no longer standby so they engaged the Corinthians. However, the Corinthians noticed an Athenian fleet of twenty new warships. Apparently, a fierce debate ensued among the Athenians after the first ten ships left for the region and more ships were dispatched to the area. Not knowing how many ships could be over the horizon or enroot the Corinthians decided to disengage. The next day the Corinthians pulled-out of the area because they worried that Athens would consider the skirmish the beginning of a full-on-war.[12] Corinth could not win a war against Athens without the support of Sparta. The Athenians allowed them to leave peacefully. The minimal effort plan (defensive only) had failed and Athens now had to prepare for war.[13]

Comparing the Theories

Athens ended up losing the war. The focus from this point will be on the details and action which had the most impact. There are distinct actions during the Peloponnesian war which Clausewitz’s theories warns against. None of Aquinas’ theories on “just war” were considered by Sparta or Athens, fear and suspicion ruled both sides. Perhaps Sun-tzu’s concept regarding a failure in politics holds true, i.e. war is a consequence of failed political negotiations. Of course, with the exception of Sun-tzu (around 512 BC) these theories had not been developed.[14] But that’s not the point. It’s important to realize that these theories were chosen for this reason—they are not constrained by time periods in history nor the future. They do not function like applications relevant to the current technology of the era but they are properties of a continuity derived from complex human experiences extending back to at least the beginning of civilization. This is not an argument for some type of transcendent mystical force at work in the physical world. These properties from which the theories were realized had probably always existed with humanity but it took a certain mind(s) to recognize and articulate their place as civilizations evolved and clashed.

Clausewitz’s goal was to explain war as a universal phenomenon.[15] His theory on war involved universal principles that could apply to war itself. In this sense the theory holds true regarding past and future warfare. Clausewitz viewed war as a tool to accomplish political goals; technology does not alter this reality in modern warfare. In book eight, chapter two of On War Clausewitz states, “the overthrow of the enemy is the natural end of the act of war; and if we would keep within the strictly philosophical limits of the idea, there can be no other in reality.[16] These ideas apply to ancient warfare as well. Another important concept from Clausewitz’s theories was the idea of “absolute war”. He insisted that a war with no limits, “absolute war” is the only war in which armies should engage and that limited war should only be limited by nature, not by choice. A good example of war limited by nature is natural barriers that would prevent access to adequately engage with the enemy, impassible terrain—mountains, swamps, rivers, etc.[17] This concept will become more apparent in the Soviet-Afghan War section of this analysis.

The Athenians were reluctant to agree to a full alliance with the Corcyraeans instead they elected to a limited position—defensive alliance only. Kagan contemplates Athens’ decision to practice limited warfare in his book. Kagan hypothesized, “perhaps a full offensive and defensive alliance such as the Corcyraeans proposed would have convinced the Corinthians that Athens was serious.”[18] Nevertheless, when Sparta and Athens went to war the Athenians took mostly a defensive position. These two actions proved to be not only a violation of Clausewitz’s theories but the primary factors contributing to Athens’ defeat. Sun-tzu’s theory on war was to subjugate your enemy without actually engaging in combat. He emphasized diplomacy and coercion, to manipulate and frustrate the enemy, and to only resort to armed combat when the enemy threatens the state with military action.[19] Diplomacy had failed but Athens continued to employ a defensive strategy. Aquinas’ principles on the justification for war were also ignored. Neither side was guilty of inflicting evil on the other, therefore, neither side had justification to wage war. The Athenians and Spartans were influenced by fear and suspicion of each other magnified by their allies’ rhetoric. They both were, however, concerned with gaining influence and power in the region; if for no other reason than to check the power and influence of the other. This was another infringement on Aquinas’ principles—never engage in war for the purpose of gain.

[1]Hew Strachan, Clausewitz’s On War: A Biography (New York: Grove Press, 2007), 3.

[2] Carl Von Clausewitz, On War (1832), Translated by Colonel J. J. Graham (New York: Barns & Noble Inc., 2004), 3.

[3] Thomas Aquinas, Summa Theologica: On Law, Morality, and Politics Translated by Richard J. Regan, 2nd ed., (Indianapolis, IN: Hackett Publishing Company Inc., 2002), 165.

[4] Brian Todd Carey, Warfare in the Ancient World (South Yorkshire: Pen & Sword Military, 2013), 51.

[5] Donald Kagan, On the Origins of War: And the Preservation of Peace (New York: Anchor Books, 1995), 20. 

[6] Ibid., 21.

[7] Ibid., 24-25.

[8] Ibid., 27.

[10] Ibid., 43-45.

[11] Ibid., 47.

[12] Thucydides, The Peloponnesian War, translated by Martin Hammond (New York, NY: Oxford University Press, 2009), 24-27.

[13] Ibid., 48.

[14] Ralph D. Sawyer, The Seven Military Classics of China (New York, NY: Basic Books, 2007), 149.

[15] Hew Strachan, Clausewitz’s On War (New York, NY: Grove Press, 2007), 77.

[16] Carl von Clausewitz, On War, 666.

[17] Ibid.,452-459, 474-489, 493-498, 66-669.

[18] Donald Kagan, On the Origins of War, 74.

[19] Ralph D. Sawyer, The Seven Military Classics of China, 154.

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