Prussian military theorist and general Carl von Clausewitz wrote On War (Vom Krige), his main work, between 1816 and 1830. His wife, Marie von Brühl, edited and published his works, including On War, shortly after Clausewitz’s death in 1831. The book remains one of the most important texts on military strategy, tactics, and war studies in general, even in the 21st century.

This guide uses the edition translated by Colonel J. J. Graham (1808-83). He was the first English translator to work on this text, with his translation appearing in 1873. Citations in the guide refer to the Kindle version of the 2009 edition published by Military Strategy Books.

Plot Summary

On War comprises eight Books, with each split into several brief chapters. The first six Books are complete; the last two Books are described as “sketches” because Clausewitz did not complete his magnum opus. Each Book addresses one distinct aspect of warfare. Book I is about the overall nature of war. Book II discusses war theory. Book III addresses the questions of strategy. Book IV is about combat. Book V analyzes military forces. Book VI, the longest book with 30 chapters, examines the subject of defense. Book VII is about offensive actions. The final Book addresses making war plans. Stylistically, On War features the typical formalities of 19th-century language, including the long sentences translated from the German original.

The author illustrates his text with examples throughout. The two historical military commanders who are mentioned the most are Frederick the Great of Prussia and Napoleon Bonaparte (See: Key Figures). These leaders are important to Clausewitz’s emphasis on military genius. Napoleon is of particular interest because of the author’s first-hand, formative experience in the Napoleonic Wars (1803-1815). Clausewitz’s breakdown of certain events, such as the Battle of Torgau (1760) or the Battle of Borodino (1812), serves as important historical analysis. However, most of these examples are limited to the late-18th and early-19th centuries and feature the wars between empires or early nation-states. Other types of wars, such as revolutions and insurgencies, are mentioned only in passing.

Several key themes recur throughout the book. Human psychology—which the author calls “moral forces”—is an important factor in warfare that had been generally overlooked at the time of writing. Clausewitz argues that the human mind is a subjective factor that may change the outcome of a battle or even the entire war. Clausewitz also anticipates the arrival of 20th-century “total war,” involving the entirety of the population, resources, and infrastructure when he suggests that wars require the armed forces, the support of the country, and the allies, or when he discusses the people’s war and guerilla tactics. Furthermore, the author’s concept of destroying an enemy’s army to impose one’s political aims is still used in the 21st century: “The military power must be destroyed, that is, reduced to such a state as not to be able to prosecute the war” (13).

Another focal point centers upon the differences between tactics and strategy—where the two converge, and where they remain separate. For Clausewitz, strategy is “the theory of the use of combats for the object of the war” (42). In this framework, the object of war is usually an overarching political goal for which the occupation of land is only a means. In turn, tactics are “the theory of the use of military forces in combat” (42). The complex relationship between tactics and strategy and between the defense and the attack feature Clausewitz’s dialectical approach to concepts. After all, every defense contains offensive actions. His very definition of war, as a duel and as a political instrument, is shaped according to the dialectical method.

Whereas this book examines the theory of war, Clausewitz emphasizes the importance of combat experience. The author argues that no books or even field training could replace a soldier’s participation in a war, and that it is from real-life experience that theorists should generalize war theory. However, he adds that there are limits to theory. In addition to the aforementioned psychological factors, chance, luck, probability, and uncertainty all affect the course of a single battle or even the entire war event.

Overall, Clausewitz perceives war as a natural social state, arguing, “Peace seldom reigns over all Europe, and never in all quarters of the world” (40). For this reason, it is best to be prepared for it. On War remains a seminal text on war theory that offers both historical documentation and insights relevant today.