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Summary: On War: Observations on the Nature, Theory & Strategy of War & Combat by Carl von Clausewitz

  • The book is a classic work of military theory that examines the nature, theory, strategy, tactics, and forces of war, as well as its political, moral, and historical aspects.
  • The book argues that war is a complex and dynamic phenomenon that cannot be reduced to simple rules or formulas, but rather depends on human factors such as passion, reason, and chance.
  • The book introduces several influential concepts in military thought, such as the center of gravity, the culminating point of victory, the fog of war, and the friction of war.

On War (1832) is widely considered to be a landmark book on the subject of war. In its serious and thoughtful consideration of why and how states engage in warfare, it continues to be an influential piece of writing centuries later.


History, Politics, Humanities, International Relations, Military History, Military Sciences

Introduction: Gain a deeper understanding behind the historical purposes of war.

The British philosopher Bertrand Russell once said, “War does not determine who is right – only who is left.” A lot of us continue to wonder why, in this day and age, nations are still attacking other nations and lives continue to be lost in armed combat. Even though it was written nearly two centuries ago, Carl von Clausewitz’s book continues to offer useful insights into the all too human endeavor of war.

The veteran Prussian general had plenty of experience during the Napoleonic Wars and took a very intellectually rigorous approach to the subject. As a result, his book is in some ways like an ongoing conversation, attempting to look at all sides and weigh all the opposing arguments. It’s a challenging work, made all the more so by the fact that it was unfinished when the author died. We’ll sift through this classic tome together and look at some of the most important and most relevant conclusions the author came to.

[Book Summary] On War: Observations on the Nature, Theory & Strategy of War & Combat

In these summaries, you’ll learn

  • how tactics and strategy can be distinctly different;
  • why critics often take the wrong approach when studying past battles; and
  • how boldness can be both an advantage and disadvantage in war.

War is about disarming your opponent through force, and it requires great presence of mind.

Before we dive into the heady subject of nineteenth-century warfare, let’s take a quick moment to break down the text. Carl von Clausewitz’s On War is divided into four sections. The first deals with establishing an agreed-upon definition for war, the second gets into theory and criticism, while the third and fourth sections touch upon strategy and tactics. So, let’s follow Clausewitz’s lead by looking at four chapters that grab some of the main points from each section.

The first question is: What is war? The author boils it down to its most basic elements and says that war is essentially a duel that is carried out on a large scale. He also compares it to a wrestling match, in that we have two forces, each attempting to bend the other to its will. The goal for both sides is to reach a point where the other is incapable of fighting any further. More often than not, this means that the goal is to disarm the opponent.

How is this goal achieved? In one word: violence. These days we have culture wars and information wars, but in the context of the early nineteenth century, the war we’re talking about is by its very nature violent. It uses physical force to achieve its ends. For the most part, we’re still talking about two armies, with columns of soldiers, squaring off against each other on a battlefield.

Now, this leads us to one of the first of moral quandaries. Every step of the way, the author is interested in exploring the moral issues of war. And right from the get-go, we find ourselves faced with a tricky question. Let’s say that we admit that war is an inescapably violent affair. How violent must it be? Even back then, there were some folks who believed that a war could be decided with a minimum amount of bloodshed. The author, however, isn’t convinced. In fact, he cautions that such an approach would likely backfire. If the goal is the disarmament and bending of your opponent’s will, then using your physical power to its utmost extent is the only logical approach. As the author sees it, the idea of moderation in war is absurd.

Clausewitz continues to define war in other ways. He makes a point of stating that war isn’t a single battle, nor is it an isolated event. For every war, there’s a backstory of events and political decisions that led up to the conflict. Therefore, we can see war as a matter of reciprocal actions. This means that every step of the way, each side is reacting to the other. Each side must make judgments on how best to react. But for the most part, there’ll be an escalation during this process until war is declared and one side is disarmed.

That said, it’s important to note that the result of a war is never the final word. If you disarm your opponent today, that doesn’t mean they won’t rearm and attack you again tomorrow. In fact, whatever hostility they felt toward you before may be small potatoes compared to the anger they feel after being defeated. This anger and fierce resentment shouldn’t be underestimated, either. Such motivations of spirit can be a deciding factor in an army’s performance.

This circles back to the author’s insistence that war is a matter of using utmost power. Leaving your opponent well-armed and capable of resuming their attack just doesn’t make sense. This also touches upon another important characteristic of war: the unknown. Some people credit Clausewitz with popularizing the concept of the “fog of war.” Indeed, it’s often the case that neither opponent fully knows the full extent of the other’s armament, their position, or how many soldiers they have in reserve. As a result, commanders are often forced to make decisions with incomplete information. This fact can also be seen to support the idea that one uses their utmost power as a general rule.

The lack of complete information also plays a large role in determining the qualities that make the best military commanders. What makes someone a military genius? While it should go without saying that a commander be intelligent, and have a keen understanding of human behavior, one must also be able to overcome the physical danger and suffering that goes hand-in-hand with war.

He describes war as a “great conquest over the unexpected,” and for this reason, he cites courage as a primary quality of a great leader. Courage in the face of physical danger, but also in the face of moral responsibility – in making tough decisions. One must be both firm and resolute, and calm under pressure, but also willing to take quick and bold action when faced with the unexpected.

In other words, a great commander needs a steady presence of mind. All the qualities of war – the danger, the suffering, the chance, the unknown – these are all things that can lead to a mind being consumed with doubt, which is about the worst thing a military commander can have.

Leaders also need to grapple with what the author considers the primary “friction” of war, which is that the aims of war are usually simple while achieving those aims is often incredibly difficult. This is one of the last points he makes in the first section. And it’s a good note to leave on as we head into the second chapter. In many ways, war is simple. Like a wrestling match. But in other ways, it’s infinitely complex.

Tactics are the science of war, while strategy is more of an art.

In Book Two, the author shifts gears a bit and starts to zoom in on the nuts and bolts of war. It’s here that the author begins to ponder whether or not it’s possible to come up with an overarching theory for war. A theory that says, this is how you conduct your army and win a war.

Let’s just say, the author is skeptical that any such theory can be made, if for no other reason than there are simply too many variables. As we’ve already discussed, too much of war rests on chance and making decisions based on incomplete information. But that doesn’t mean there aren’t aspects of war which could be turned into theory.

Book Two is where we get into the important distinctions between tactics and strategy. As Clausewitz defines it, tactics is an area where we could apply theory. Tactics involves broad things like training, running drills, and making sure your soldiers are prepared and ready. Tactics is about knowing where to establish camps and how many reserves you want to keep in waiting. In a way, tactics can be scientific.

Strategy, on the other hand, is more of an art, and therefore ill-suited to the establishment of a unifying theory. Keep in mind, war is not a single event. It’s made up of multiple decisions and battles. It’s a constantly changing thing, and the winning strategy will be the one that responds to unexpected developments as they happen. We can make rules about when one should and shouldn’t deploy one’s cavalry, but there is bound to be an exception to that rule at some point.

Often, theories emerge when we take a critical look back at a previous battle. For instance, we might look at something Napoleon Bonaparte or Frederick the Great did and try to turn it into a rule. The problem is, we often look at their battles as isolated things. It’s easy to look back to 1797 and criticize the time when Bonaparte advanced against Archduke Charles and crossed the Norican Alps. We now know how many forces Bonaparte had, as well as how many forces the Austrian Empire had. So we can sit back and point and say, well Bonaparte should have done this or was being reckless when he did that. But this kind of criticism isn’t helpful or insightful.

At the time, Bonaparte didn’t know what we know now. And we must also remember that every general’s decisions are influenced by what came before. We must refrain from analyzing a battle in isolation from the politics and situations that came before. The conduct of war can’t be understood or properly criticized when a battle is looked at as being self-contained. It is not.

So, while tactics and strategy are indeed important parts of war, they must be looked at within the big picture. How will they be applied to the many different activities, purposes, and battles that make up a war?

In the next chapter, we’ll take a closer look at strategy and the different approaches a commander can take to achieve the goals of war.

There are many strategies to consider, but success still requires soldiers of great character.

As we move on to Book Three, we find ourselves deep into the subject of strategy. Aside from being considered the true art of war, the author also defines strategy as “the deployment of battle as a means to attain the end of war.” And by the end of war, we mean, to get what you want – otherwise known as the object of war.

So, once again, we can see that there’s no one-size-fits-all strategy. A successful one must be specifically designed for the main purpose of the war in question. A perfect strategy is one that doesn’t come up short or overreach in attaining its goal. Some critics will look at Frederick the Great’s 1760 campaign and marvel at the individual marches and maneuvers. But the real marvel is that the King did just enough – no more, and no less than what was needed to bring peace.

Here’s where we should point out, however, that even the best strategy will hardly stand a chance without an army that embodies the principles of military virtue. The author defines military virtue as more than just bravery and more than just having an enthusiasm for war. As he puts it, when a man leaves himself and becomes one with the spirit and nature of the army’s purpose – to completely understand the role he needs to play and to execute that role to its fullest extent – that’s military virtue. And no matter what strategy Bonaparte, Frederick the Great, or Alexander the Great had, they wouldn’t have found success without an army that embraced military virtue down to the very last soldier. Along these lines, the author also cites perseverance, or the ability to withstand the endless pains and exertions of war to outlast your opponent, as another key trait in a successful strategy, and surely another example of military virtue.

Many of the great commanders in history also shared the gift of boldness. Now, while you might think of boldness along the lines of bravery – something a leader either has or doesn’t have – boldness is also part of the strategic art of war. You can’t just go into battle and be bold. For it to work, it requires an opening on the part of the opponent. An invitation to boldness is required, which is why a commander must have that highly attuned presence of mind to notice these chances when they arise and take advantage of them.

Speaking of the art of war, there’s perhaps no better example than stratagem. Stratagem is the deceitful side of war. A way of fighting that isn’t at all straightforward and more like a sleight of hand. As with boldness, a successful stratagem often requires unwitting participation from the opponent. Knowing something of human nature, as well as something about how your opponent thinks, will go a long way to setting up and pulling off this sleight of hand. It is, after all, a matter of setting the bait, knowing how your opponent will react, and using that to your advantage.

One of the more popular wartime stratagems is surprise. To catch your opponent off guard and be where they don’t expect you to be. For this, your opponent’s boldness can be used against them. You can give a false invitation, luring them to attack and exposing your opponent’s army, only to have them easily outflanked by your own waiting forces.

Such devious means of combat are usually deployed when other strategies have failed. But when done to perfection, a clever stratagem can have the effect of rekindling the flame and turning the tides of war back in your favor.

Victory is achieved through more than just physical losses.

Since On War was unfinished upon the author’s death, it may not come as a surprise to know that the final section, Book Four, is quite smaller than the other three. Here, the author dives into the “characteristics of the modern battle.” So we once again zoom in, and rather than looking at the big picture of war, we’re looking at what goes on in a single battle.

In the previous chapter, we talked about military virtue and perseverance. Clearly, the author is well aware of the importance of troop morale. So it stands to reason that many of the characteristics the author mentions in Book Four touch upon the kind of tactics and strategies that can chip away at your opponent’s morale and wear them down into submission.

Now, of course, when Clausewitz talks about “modern battle” he’s talking about early-nineteenth-century battle. This was the time when two forces, camped out about a day’s march from each other, would square off on a battlefield. Indeed, this was a time when warfare would usually begin at the break of dawn and end at nightfall after a long and grinding day of fighting. For the most part, neither side would want to waste artillery shooting at things you couldn’t see, or run the risk of blindly walking into a battalion of your opponent’s forces.

The author takes great pains to once again assert that the object of both wars and battles is the destruction of your opponent’s army. To wear down your opponent to the point where they can no longer continue the fight. There are many ways in which an army can be made to suffer. Loss of men, horses, and guns is one thing, but an army’s courage, confidence, and sense of order can also be fatally wounded. And when we consider what it takes to get an army to the point of surrender, wounding their courage and morale is hugely effective.

Therefore, the author defines victory in battle through three main points: a greater loss in physical power, in moral power, and then reaching the point where the opponent admits to this greater loss by relinquishing their intentions.

Flank and rear attacks, as well as surprise attacks, have the benefit of being both destructive in a physical sense, as well as in regard to morale. Nighttime bombardments can also take a mental toll. By firing off heavy artillery in the direction of the opponent’s camp, you’ll be keeping the opponent on edge, and perhaps forcing them to be constantly on the move rather than getting any rest.

Oddly enough, a short chapter on night fighting is how the book comes to an abrupt end. There’s no grand summation of ideas to go out on. But Clausewitz does raise a question in this final section that continues to be relevant today: Can there be such a thing as a bloodless war? In his estimation, no. As the author says, “If a bloody slaughter is a horrible sight, then let that be the grounds for paying more respect to War.” If we remove the edge from our swords due to feelings of humanity, it’s only a matter of time before someone with a sharp sword comes along and makes us pay a painful price.

Final Summary

We’ve come to the end of our summary to On War, by Carl von Clausewitz.

The most important thing to remember from all this is this:

War is simple, and yet it’s complex. The object is straightforward enough: to disarm your opponent with force, thereby forcing them to bend to your will. But there’s no straightforward way to reach this goal. There are tactics and training you can fall back on, but finding a successful strategy is an art form. It takes a commander with presence of mind, and an army made up of strong characters who can persevere through the hardships and dangers involved. Dealing with chance and the unexpected are routine challenges. And when it comes to victory, wearing down the morale of the opposing army can be just as important as doing physical damage.

About the author

Peter Paret is professor emeritus at the Institute for Advanced Study in Princeton. His many books include Clausewitz in His Time, The Cognitive Challenge of War (Princeton), and Clausewitz and the State (Princeton). He is a recipient of the Pritzker Literary Award for lifetime achievement in military writing. Michael Howard (1922–2019) was a leading British military historian who held professorships at the University of Oxford and Yale University. His many books included The Franco-Prussian War and War in European History. Bernard Brodie (1910–1978), who wrote widely on military and nuclear strategy, was professor of political science at the University of California, Los Angeles.


On War is a classic work of military theory, written by a Prussian general and scholar who participated in the Napoleonic Wars. The book is divided into eight books, each covering a different aspect of war, such as its nature, theory, strategy, tactics, forces, defense, offense, and planning. The book is unfinished and was edited and published by the author’s wife after his death.

The main theme of On War is that war is a complex and dynamic phenomenon that cannot be reduced to simple rules or formulas. Clausewitz argues that war is an extension of politics by other means, and that its ultimate aim is to impose one’s will on the enemy. He also emphasizes the role of human factors, such as passion, reason, and chance, in influencing the course and outcome of war. He introduces several concepts that have become influential in military thought, such as the center of gravity, the culminating point of victory, the fog of war, and the friction of war.

Clausewitz also analyzes various historical examples of warfare, especially from the 18th and early 19th centuries, to illustrate his arguments and critique previous theories. He draws heavily from the experiences of Frederick the Great and Napoleon Bonaparte, whom he considers to be military geniuses. He also acknowledges the limitations of his own perspective and the need for constant adaptation and innovation in war.

On War is a masterpiece of military philosophy that has shaped the thinking of generations of soldiers, strategists, historians, and political leaders. It is a challenging but rewarding read that offers profound insights into the nature and conduct of war. It is also a reflection of the author’s own life and times, as well as his personal views and values.

The book’s strengths lie in its depth, breadth, and originality. Clausewitz covers a wide range of topics related to war, from its causes and purposes to its methods and effects. He also explores the moral, psychological, and ethical dimensions of war, as well as its relation to history and culture. He challenges many conventional wisdoms and assumptions about war, and proposes new ways of understanding and approaching it.

The book’s weaknesses stem from its incompleteness, inconsistency, and datedness. Clausewitz did not finish his work before he died, and left many gaps and contradictions in his arguments. Some of his ideas are unclear or ambiguous, while others are contradictory or incompatible. His examples are mostly drawn from European warfare in his era, which may not be applicable or relevant to other contexts or times. His style is also dense and verbose, which may make it difficult for some readers to follow or appreciate.

Overall, On War is a seminal work that deserves to be read by anyone interested in war or military affairs. It is not a manual or a guidebook for war, but rather a philosophical inquiry into its essence and implications. It is a book that challenges one’s assumptions and stimulates one’s imagination. It is a book that invites one to think critically and creatively about war.

Alex Lim is a certified book reviewer and editor with over 10 years of experience in the publishing industry. He has reviewed hundreds of books for reputable magazines and websites, such as The New York Times, The Guardian, and Goodreads. Alex has a master’s degree in comparative literature from Harvard University and a PhD in literary criticism from Oxford University. He is also the author of several acclaimed books on literary theory and analysis, such as The Art of Reading and How to Write a Book Review. Alex lives in London, England with his wife and two children. You can contact him at [email protected] or follow him on Website | Twitter | Facebook

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