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How is it possible that defenders are responsible for most wars? Why is it a logical contradiction for military concerns to influence political policy? And why shouldn’t soldiers sleep in tents?

Carl von Clausewitz answers all these questions and more in his treatise On War. While it was originally published in 1832, Clausewitz’s philosophical underpinnings of war are arguably still relevant in the modern day.

Below is a brief overview of the key themes and takeaways from On War by Carl von Clausewitz.

The Purpose of War

On War by Carl von Clausewitz is an exploration of the philosophy of war as a political and a societal phenomenon.

According to Clausewitz, war is nothing but a tool of politics. When different nations or groups have conflicting political interests, one way to make the other side accommodate your interests is to compel them by means of military force. This, then, is the purpose of war: to force the enemy to comply with some kind of political demand. For example, maybe one country demands control of a region currently controlled by another country and invades that region if the other country refuses to cede it. Or perhaps an interest group within a country demands governmental reform and starts a revolutionary war if the government doesn’t reform.

(Shortform note: Robert Greene turns this definition of war around and uses it as the basis of his book The 33 Strategies of War. Where Clausewitz says the purpose of war is to compel someone (typically the leader of a rival nation) to yield to political demands, Greene says that any attempt to compel or control someone is itself an act of war. As such, he argues that you can apply strategies developed for military operations in any area of life where people may try to control you, such as work and business.)

Defenders Make Wars Happen

As Clausewitz points out, his definition of the purpose of war implies that, as counterintuitive as it sounds, war is generally caused by defenders, not aggressors. This is because aggressors don’t directly make war; they only make political demands and perhaps send troops to enforce their demands. If the defender gives in to their demands without a fight, then the war doesn’t happen.

War Can Be Misused 

Of course, war is not the only tool for advancing political interests. Clausewitz would probably agree that you shouldn’t resort to war if you can achieve your political purpose by other, less extreme measures. He does point out that, while war is a tool of politics, politicians don’t always use it correctly. Sometimes they start wars that achieve the opposite of what they wanted to achieve. 

(Shortform note: Some experts argue that war and a combative mindset are usually counterproductive because they provoke others to resist you. In The Anatomy of Peace, the Arbinger Institute argues this point and proposes a strategy for getting others to accommodate your interests or demands without resistance by first building a relationship with them based on a cooperative mindset. They develop this strategy mostly in the context of interpersonal relationships, but some elements of their strategy could apply to international relations as well.)

War Should Be Subservient to Political Policy

Clausewitz also argues that letting military interests shape political policy or giving the military latitude to take action outside of political policy is ridiculous because war is a tool of politics, not the other way around.

(Shortform note: This is a point of disagreement between Clausewitz and Sun Tzu, who asserts that a military commander should adapt to the events of a war and do whatever it takes to win the war and protect the people of the nation, even if it means violating political policy.)

The Essence of War

As we’ve discussed, war is a tool for advancing political interests, but that is its purpose, not its essence. What differentiates war from other means of pursuing a political objective? According to Clausewitz, it’s violence. Combat is the essence of war: When two nations or factions are at war with each other, their respective soldiers are trying to kill each other. If they’re trying to achieve a political objective by any means other than killing each other, then war is not the tool that they’re using.

Consequently, Clausewitz completely dismisses the idea of trying to make war less violent. Since war is violence, any attempt to make it less violent is delusional. By all means, find non-violent ways of achieving your objectives if you can, but if you must resort to war, then you must resort to violence.

He goes on to point out that even a “bloodless victory,” where the enemy retreats without firing a shot, still depends on your willingness and ability to engage in combat: Your enemy only withdraws because he has no hope of winning, or because the cost of winning would be unacceptably high. Either way, your capacity for violence is what drives your enemy to seek peace.

The Study of War

In addition to discussing the purpose and essence of war, Clausewitz frequently comments on the academic study and theory of war. He expresses dissatisfaction with common theories of his day, asserting that they didn’t provide an accurate model of real war, and he identifies three key shortcomings that tend to undermine their accuracy. He admits that these factors are difficult for a theory to predict and clarifies his discourse on war is not intended to provide a comprehensive model of war.

1. War Doesn’t Take Place in a Vacuum 

As we discussed, war is a political tool, so the political motives behind any given war will shape the events of the war. Thus, a theory cannot model war accurately if it treats it as a self-contained phenomenon, independent of the cause or purpose of the war.

2. War Is Human 

Psychological resources like the motivation, resolve, and emotional strength of an army play an even more significant role in winning battles than physical resources like the number of soldiers and the supply of ammunition. 

Furthermore, war is intensely personal for those involved: Even if the war was started for the purpose of advancing an impersonal political cause, once the soldiers have seen a few of their friends killed in action, they inevitably come to hate the enemy at a personal level. Thus, a theory cannot accurately model war if it treats soldiers and commanders as impersonal or perfectly rational beings.

3. War Involves Uncertainty 

In a real war, you never have complete information about your enemy’s strength, position, or plans, and the information you have is usually wrong. It may be outdated or distorted by human biases of the people who gathered or relayed the information. In particular, people tend to over-report bad news and under-report good news, so your enemy is often a lot weaker than the latest intel indicates. 

When you command an army, even the actions of your own troops are subject to a measure of uncertainty because your orders can be misinterpreted as they’re passed down the chain of command. Then there’s always an element of luck involved in carrying them out. Any number of unpredictable factors beyond your control can affect the success or speed of your operations: Maybe some of your gun carriages get stuck in the mud and that delays getting your artillery into position. Maybe a fog bank rolls in, and you can’t see important landmarks that you were using to plot the course of a march. Maybe there’s an outbreak of sickness in your camp. 

Thus, a theory that assumes both sides have perfect information and can predict each other’s actions and maneuvers, or even their own, with reasonable precision cannot provide an accurate model of war.

Tactics and Strategy in a Model War

Now that we understand Clausewitz’s views on what war is, what it’s for, and the difficulty of developing theories that are faithful to the reality of war, we can consider his practical advice on tactics and strategy from his viewpoint. 

To understand his advice, it’s also helpful to picture the context in which he meant it to be applied. Documenting the normal operations of the military in his day was not Clausewitz’s primary purpose in writing, but he mentions many aspects of these operations in passing. And since the normal operations of armies in the Napoleonic era are no longer common knowledge (as they would have been to Clausewitz’s original audience), we’ve used the information that he provided in passing to describe a hypothetical war, which should furnish the necessary context.

However, before we dive into our hypothetical war story and use it to present Clausewitz’s ideas about tactics and strategy, we need to clarify what he meant by “tactics” and “strategy.”

The Relationship Between Tactics and Strategy

Throughout the book, Clausewitz is careful to differentiate between strategy and tactics. Strategy is about picking your battles to achieve the ultimate objective of the war. Tactics are about winning any particular battle, given the troops you’ve got to work with, the terrain, your enemy’s position, and so on. 

However, despite Clausewitz’s efforts to continually distinguish between the two, his discussion makes it clear that tactics and strategy are not independent of each other. Tactical considerations such as the type of terrain and which troops can make better use of it affect the likelihood of winning a given battle, which in turn affects your strategy: You would probably try to avoid a battle if tactical factors favor your opponent. And the strategic purpose of a battle may affect your tactics. For example, you’ll use different tactics if your goal is to defend a key position with minimal losses than if your goal is to wipe out a particular enemy force at any cost.

Because tactics and strategy are actually interwoven in war, Clausewitz’s insistence on distinguishing between them may, at times, be more distracting than useful. As such, we will present his tactical and strategic advice largely without differentiating between the two.

Initial Preparations and Organization

For the remainder of this guide, imagine that it is the early 1800s. You are in command of the army of Country A, and Clausewitz is your advisor. Neighboring Country B recently broke off political negotiations on an issue of vital importance to your country, and war has been declared. 

Your mission is to defeat B’s army and occupy their capital. As Clausewitz explains, every nation’s strength revolves around something—usually either their government or their military. So, by defeating their army and taking over the seat of their government, you’ll most likely render Country B powerless to refuse the political terms that would secure your nation’s interests.

(Shortform note: A similar principle is commonly used in “hardball” business strategies for dealing with competitors. Just as a nation’s strength typically comes from a few key sources, every company has certain products or services that net them most of their profits. Identifying your competitors’ most profitable products allows you to compete more effectively, whether by taking a share of a particularly profitable market or tacitly agreeing to stay out of their market as long as they stay out of yours.)

Organization of Your Army

Your army consists of infantry armed with muskets, cavalry armed with sabers, and muzzleloading cannons for artillery. On Clausewitz’s advice, you organize your troops into eight groups, with units of infantry, cavalry, and artillery in each group. This gives you maximum flexibility by giving each group all the capabilities it needs to fight independently from the other groups if needed.

(Shortform note: Clausewitz assumes a centralized command structure and advises fully equipping each group to give the commander maximum flexibility. But some modern-day military commanders, such as US Navy Captain David Marquet, advocate not only giving troops more capability to carry out orders but empowering them with the authority to respond to situations as needed without waiting for orders.)

This strategy also keeps the hierarchy of command as flat as possible. The fewer people who have to pass on your orders before they get to the individual soldiers, the less chance of them being distorted or misunderstood. But according to Clausewitz, eight to 10 subordinate commanders reporting to you directly is about the most that you can realistically keep track of.

(Shortform note: Modern business writers echo Clausewitz’s admonition to keep organizational structures relatively flat for better communication between all levels of the organization. Interestingly, management experts like Andrew Grove (former CEO of Intel), also agree that eight direct reports is about the most that you can really manage, despite the vastly different circumstances of managing a technology company in the 21st century versus commanding an army in the 19th century.)

Mobilization and Supply

As you move your army toward B’s border, you spend about half of each day marching and the other half dealing with supply issues. You purchase most of the food and other common supplies for your army from the local people as you move through your country or collect it from local government officials who’ve purchased it for you. You lodge your troops in whatever dwellings happen to be nearest to your route. As Clausewitz explains, these practices save considerable time and effort relative to sourcing all your supplies through military supply lines and setting up campsites all along the route of your march. Besides, in your own country, the local people should consider it part of their civic duty to feed and house soldiers passing through.

(Shortform note: While housing troops in civilian homes along their route may have been convenient for the military, even in Clausewitz’s day, some people viewed it as an invasion of privacy and a burden on the civilian population. This sentiment is reflected in law: The English parliament prohibited housing troops in civilian homes without the voluntary consent of the homeowner in the 1680s. And the Third Amendment of the US Constitution similarly restricts quartering soldiers in civilian homes.)

Sourcing Food in Enemy Territory

Once you cross the border into Country B, you need to adjust your routine. You still get most of your supplies from the locals, but now you do so by sending soldiers to the local officials and demanding that they give you what you need. Clausewitz notes that this is not only the most efficient way of sourcing food and common supplies, but it also has the added benefit of weakening your enemy since you’re now feeding your troops on B’s resources instead of your own.

That said, Clausewitz also stresses that it’s important to move quickly through enemy territory because your army will exhaust all the local food supplies if you stay in one place too long. And if you run out of local supplies, bringing them all the way from your home base in wagons is risky and expensive.

To allow for unforeseen delays or emergencies, he recommends having every soldier carry four days’ rations in his own pack and keeping another four days worth of food for the whole army in supply wagons that move with the army. That way, if the need arises, you can travel or fight for up to eight days without any new supplies.

Lodging in Enemy Territory

Clausewitz says that if you’re confident that Country B’s army is too far away to threaten you with a sudden attack, you can still quarter your troops in local housing on foreign soil. This is an efficient way of living off the enemy’s resources. 

(Shortform note: In business, an analogous tactic is making use of your competitors’ services to get people to use your product—initially in addition to your competitor’s product, and eventually instead of it. For example, as a startup, Airbnb made use of Craigslist (a competitor in peer-to-peer property listings) both to identify prospective hosts and to cross-advertise listings.)

However, as the likelihood of encountering B’s armed forces increases, he says you should transition to making camp each night. In camp, the army remains together instead of spreading out to shelter in different houses. This provides better security, since your night watchmen don’t have to patrol as large an area, and your soldiers can assemble for battle more quickly.

That said, even when you’re planning on making camp, Clausewitz advises against bringing tents for the soldiers to sleep in. This is because it takes many horses to carry enough tents for an army, and those horses could serve you better in the cavalry than in the supply train. He assures you that bivouacking (camping in the open air) won’t degrade your troops’ health or fighting ability.

Winning a Battle 

Let’s say the first resistance you encounter is a chain of outposts guarding a river that you must cross on your way to B’s capital. As Clausewitz points out, the river limits how fast you can move your troops into position to attack the enemy forces because it takes time to build a bridge or ferry your troops across the river. This gives B’s defending forces an advantage. 

However, he also says that, in this case, it’s not a major problem because your army significantly outnumbers the enemy force. Strength in numbers is more consequential than the advantage or disadvantage that terrain features like this afford. In particular, Clausewitz assures you that outnumbering your enemy by at least two-to-one practically guarantees victory in most cases.

Moreover, this situation actually amplifies your numerical advantage, because the defending force is strung out over a long stretch of river. They don’t know where you’ll try to cross the river, so they have to guard its whole length. But you can bring your whole force across at one place. This way, you’re using your whole force against a small portion of theirs. 

Using Reserve Troops to Reenergize Your Forces

Let’s say you ferry enough infantry across the river in boats to hold a position on the far bank while your army builds a makeshift bridge. The bridge allows you to bring the bulk of your force across the bridge before B’s whole defending force can converge on your location. 

But, on Clausewitz’s advice, you don’t send all your troops into battle at once. Instead, you send just a few more than the enemy appears to be fielding and keep the rest far enough back to be out of the battle. Clausewitz calls the troops that you don’t initially send into battle your “reserve force,” and it can serve a number of functions. For one thing, there’s always some uncertainty about how a battle will unfold, so it’s good to have troops ready that you can send in to counter the enemy’s unforeseen moves. 

Moreover, you can use them to reinforce and refocus your troops in combat: Clausewitz observes that battles often open with focused, coordinated fighting but quickly devolve into disorganized, reactive fighting because soldiers easily forget their plans and orders under the stress of combat. If you send in fresh troops after the fighting has become disorganized, they can help all your forces refocus on their battle objectives. If the enemy forces have become disorganized by this point as well (and don’t similarly refocus their forces with fresh troops), this gives you a huge advantage and usually results in a decisive victory.

(Shortform note: Sun Tzu also suggests holding back a few of your troops to counter your enemy’s unforeseen moves or exploit enemy weaknesses that become apparent later in the battle. And he discusses the importance of psychological factors in battle. But he doesn’t combine the two as Clausewitz does when he recommends sending in reserve troops to refocus your attack.)

Finally, when you win a battle, you can use your fresh troops to pursue the enemy.

Making the Most of Victory by Pursuing the Enemy

As soon as the enemy begins to retreat from the battlefield, Clausewitz urges you to pursue them. Take possession of any cannons or supply wagons that they abandon in their haste to get away, take any stragglers prisoner, and keep the retreating army under fire so they never have a chance to rest and regroup. 

Ideally, he says your army should follow B’s retreating force until they try to make camp for the night and then attack their camp, forcing them to retreat again. Then, your army can make camp and get a good night’s rest while B’s army marches through the night, unable to see if you’re still on their heels. If you can catch up with them and attack their camp again the next day, then they’ll have to march through the night again, and so on. 

(Shortform note: Modern science supports the effectiveness of weaponizing sleep deprivation as Clausewitz advises. As Bill Bryson notes in The Body: A Guide for Occupants, studies have shown that sleep deprivation can be fatal. Lab rats that are prevented from sleeping die within a month, and in humans, genetic disorders that make sleep impossible also lead to death. Thus, in principle, Clausewitz’s tactic of preventing the enemy from sleeping by attacking their camp each night could directly inflict massive casualties if you kept it up long enough.)

The Turning Point of a War 

You continue to chase the remnant of B’s retreating army until they reach a garrisoned fortress and take refuge there. On Clausewitz’s advice, you split your forces, leaving some troops to keep the fortress under siege, while the larger portion of your force continues toward B’s capital.

Splitting your forces is generally not a good idea, because it reduces your strength in numbers. But in this case, it’s warranted because the siege will take time, and the longer it takes you to reach B’s capital, the more time they’ll have to raise additional troops and prepare their defenses: Time is on their side. 

Clausewitz explains that invasions such as this often reach a turning point because time is on the side of the defender, while both time and distance are working against the attacker. The longer your army is out in the field, the more your force will get worn down: You lose men in battle, even when you win the battle. You also lose men while marching, as some of them won’t be able to keep up due to illness, injury, or fatigue. Finally, you lose wagons or artillery when they break down in the field or are damaged in battle. And the farther you go into enemy territory, the more troops you have to divert to protect couriers and convoys on the routes that you use to communicate with your home country.

So the longer you continue your attack, the weaker you become while your enemy becomes stronger. As Clausewitz points out, this doesn’t matter if you completely defeat your enemy while you’re strong enough to do so, which is what you’re trying to do in this case. 

But if you wait too long, or if you weren’t strong enough to begin with, then you’ll reach a point where the enemy can match your military strength. Ideally, just before you reach that point, you would break off your attack and switch to building up your defenses in the territory you’ve conquered. Then, time begins to work in your favor. But Clausewitz opines that it’s almost impossible to know exactly when you’re going to reach that turning point. He observes that most commanders either halt their attack prematurely or else press the attack until they’re badly overmatched and can’t defend what they conquered.

The Element of Surprise

As you approach Country B’s capital, you finally meet the main body of B’s army. To your surprise, you’re outnumbered by about two to three. As we’ve discussed, there is always some uncertainty in war. Clausewitz points out that other military theorists put a lot of emphasis on gaining an advantage by deceiving the enemy or attacking quickly, in the hopes of catching the enemy by surprise. 

He says that in reality, the element of surprise is overrated. The only “surprise” that really makes a difference is finding enemy troops where you didn’t expect to find them, or in greater numbers than you expected, and these kinds of surprises are usually more a matter of chance than deliberate deception.


You meet the enemy in battle, but it soon becomes clear that you’re not going to win, or at least not win a decisive victory that would allow you to achieve your political objective of crushing B’s army and occupying their capital. Clausewitz advises you to execute an orderly retreat while you can still do so with your fighting force intact.

To do this, you assemble a rear guard from your best remaining troops and use them to defend a series of defensive lines. Their orders are to hold each line for a certain amount of time and then fall back to the next line, such that B’s army is continually under fire as they pursue you.

As Clausewitz explains, this provides two major advantages, one physical and the other psychological. The physical advantage is that delaying any pursuit allows your army to retreat slowly enough that you don’t have to abandon supplies, artillery, wounded soldiers, or others who wouldn’t be able to keep up with a fast march. 

The psychological advantage is that, as the rear guard succeeds in holding off your pursuers, these little victories help to rebuild your troops’ confidence after it was shattered by losing a battle and having to retreat.

That said, Clausewitz also cautions that after losing a major battle, it’s almost impossible for an army to fully recover its confidence and morale without outside help. Usually, this outside help takes the form of fresh reinforcements: The additional troops increase the physical strength of your army, and, perhaps more importantly, this gives your army tangible reason to believe they’re no longer inferior to the enemy.

In this case, let’s say that you make it back to the fortress that you besieged and rejoin the forces conducting the siege. Meanwhile, B’s army has been weakened by the long chase and the casualties that your rear guard inflicted. Now you’re potentially able to match their strength again.


By this point, you’ve done a lot of marching, crossed a river under fire, defeated some of Country B’s forces, divided your army to lay siege to a fortress, lost a battle against B’s main army, retreated from defeat, and regrouped your main fighting force. However, instead of culminating in a decisive battle between your main army and B’s main army, the war now devolves into a stalemate: It has become apparent that, at present, you don’t have the military strength to achieve your original political objective (crush B’s army completely and occupy their capital). Yet any of B’s territory that you can occupy gives your country more to bargain with in negotiations. Meanwhile, B’s army doesn’t have the strength to crush yours with a decisive counterattack, or at least B’s commander isn’t confident that they do and isn’t willing to risk losing a decisive battle with their main force.

So you both wait for the situation to change. You send out a few raiding parties to ambush B’s supply convoys, and B retaliates in kind. Your raiding parties and convoy escorts fight minor skirmishes with each other, but you both avoid major battles. Clausewitz assures you that this is normal. In fact, situations where both sides are basically just waiting for circumstances to change make up the majority of the time you’ll spend at war.

On War by Carl von Clausewitz: Book Overview

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  • Carl Von Clausewitz’s philosophical ideas about war
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Darya Sinusoid

Darya’s love for reading started with fantasy novels (The LOTR trilogy is still her all-time-favorite). Growing up, however, she found herself transitioning to non-fiction, psychological, and self-help books. She has a degree in Psychology and a deep passion for the subject. She likes reading research-informed books that distill the workings of the human brain/mind/consciousness and thinking of ways to apply the insights to her own life. Some of her favorites include Thinking, Fast and Slow, How We Decide, and The Wisdom of the Enneagram.

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