War Classics: On War (Vom Kriege)

Patrick Mercer recalls one of the great works of military history.

Carl von Clausewitz’s seminal work of applied military philosophy is still regarded as one of the most important books of its kind. The author was Prussian, although he also served in the Russian army and saw a wealth of fighting. Following the early years of the French Revolution (when Prussia invaded France), Jena (at which Clausewitz was taken prisoner), and Borodino, his battle experience peaked as chief of staff to the Prussian III Korps at Ligny and Wavre – the crucial engagements fought in parallel to Quatre Bras and Waterloo – which led to the downfall of Napoleon. In short, Clausewitz saw more than his share of flying lead and clashing steel.

Largely written after the Napoleonic Wars, between 1816 and 1830, and published posthumously by his wife Marie von Brühl in 1832, On War (Vom Kriege) is an unfinished work. Clausewitz started to revise his accumulated manuscripts in 1827, but died before he finished, leaving his wife to edit his collected works and publish them between 1832 and 1835.

The final version is organised into eight books, which range from the nature of war, its theory and strategy, to combat and plans. Revealingly, Clausewitz deals only with attack and defence as the two major ‘operations of war’, but under those general headings he covers a plethora of settings – including attack and defence in mountains, swamps, cities, and so on. The unwary student might think that this sounds like a tactical handbook, a blueprint for every sort of encounter with the enemy: it isn’t. It’s a carefully crafted philosophy based on experience, not theory, which has allowed it to be of continued use as technology, statesmanship, and communications have evolved in the wars that have followed its publication.

Carl Philipp Gottlieb von Clausewitz

Born: 1 July 1780
Died: 16 November 1831
Nationality: Prussian

Carl von Clausewitz enlisted in the Prussian army in 1792, taking part in the French Revolutionary and Napoleonic Wars. Rising to the rank of major general, he played a key role in the reform of the army and state that followed Prussia’s defeat at Jena in 1806, and later took part (including for a period in the service of the Russian empire) in the campaigns that brought down Napoleon. He worked on the text of On War during his tenure as head of Berlin’s Military Academy (1818-1830). It was published after his death from cholera in 1831.

The author has enjoyed periods of fashion and endured criticism from thinkers and soldiers alike as warfare has changed. Since 1945, most fighting has been of ‘low intensity’ – in broad terms, uniformed armies against guerrillas – and this has led many to question his relevance.

Some of that criticism revolves around the fact that On War is not an easy read: there’s no single-page summary, and each chapter within each book rests on central tenets that need to be properly understood. It requires not just effort, but some careful thought and imagination. I’d even suggest that for serving soldiers it’s better digested once a diet of some active service has been tasted. Only after one has experienced the real pressure of lethal operations – rather than the sham of drills and exercises – can ‘friction’, ‘culminating points’, and a host of other maxims be properly understood.


As a young infantryman, I was lucky enough to be taught Clausewitz by one of his most-distinguished disciples, the military historian Michael Howard (1922-2019). Few remember that Sir Michael had won a Military Cross at Monte Cassino, and he drew on his considerable battle-experience to explain – brilliantly – the author’s logic. But it was simpler to apply Clausewitz’s concepts against the backdrop of the Apennines than among the housing estates where my colleagues and I were serving. Or was it? A purely literal interpretation of Clausewitz might justify the accusation that he was ‘the Mahdi of mass and mutual massacre’, as Sir Basil Liddell Hart famously contended. Yet even a rudimentary reading of Book VIII, Plan of War, and the chapter on the ‘Influence of the Political Object on the Military Object’, was vital for anyone involved in a counter-insurgency operation.

Similarly, Napoleon’s dictum that ‘In war, the moral is to the physical as three is to one’ is utterly Clausewitzian. Today, as ‘conventional’ European war is with us once more, this phrase has been heavily over-used by one armchair general after another. I wonder, though, how many of these pundits have studied Book III, Strategy in General, where Chapters 3 and 4 deal with ‘Moral Forces’ and ‘The Chief Moral Powers’? I’m probably being unfair, but I suspect that Clausewitz may have been damned in the past few months by some of the same people who discounted him as a creature of an era in which airpower, cyber- and space-warfare, and weapons of mass destruction had no influence, and where utter destruction of an enemy rather than his defeat was always the goal.

Yet Clausewitz was born into a realm of conflict, with his life framed by the American and French Revolutions, as well as the uprising in Ireland in 1798 – all of which spawned a new form of People’s War. The French Revolution and Napoleonic Wars led populations to new levels of guerrilla warfare, with revolution and counter-revolution becoming commonplace, and reaching a degree of effectiveness previously unknown both in terms of territorial gain and as a novel form of battle. Ultimately, ‘asymmetric warfare’ – a term that had not then even been coined – became a weighty part of combat in general, even making its contribution to the absolute character of war.

Some doubt Clausewitz’s understanding of what modern soldiers might call ‘low-intensity’ operations. They should remember, though, that not only did he analyse the savagery of guerrilla war during the counter-revolution in the Vendée region of France (1793-1796) and the Peninsular War in Spain, but he also lectured on small-scale warfare at the Allgemeine Kreigsschule in 1810-1811, using his own experience both to instruct his listeners and to clarify its principles for himself.

Despite all this, during a spirited debate at Britain’s Staff College on the relevance of Clausewitz to modern warfare, I can remember his great quote – ‘What do we mean by the defeat of the enemy? Simply the destruction of his forces, whether by death, injury, or any other means —either completely or enough to make him stop fighting… The complete or partial destruction of the enemy must be regarded as the sole object of all engagements… Direct annihilation of the enemy’s forces must always be the dominant consideration’ – being used to prove his irrelevance to operations such as those in Northern Ireland and the Basque country which were raging at the time.

Terms such as ‘annihilation of the enemy’s forces’ were taken to be overly blunt and outdated. It was thought to smack of trenches and Blitzkrieg, whereas ‘neutralisation’ was altogether more suitable for a nuanced counter-terrorist campaign. But a little analysis of that quote, and a brief application of imagination, shows just how apposite it was to the Volkskrieg – the people’s war – of today. The panoply of politics, religion and divided societies, and the complications of sensitive intelligence sources, indigenous militias, and the police, can all be cut through by the soldier who keeps the maxim that ‘The complete or partial destruction of the enemy must be regarded as the sole object of all engagements’ at the forefront of his planning.

LEFT The Battle of Jena,14 October 1806. As the Prussian army disintegrated, Clausewitz was captured. He was then imprisoned in France from 1807 to 1808.
The Battle of Jena,14 October 1806. As the Prussian army disintegrated, Clausewitz was captured. He was then imprisoned in France from 1807 to 1808.


Moving from small wars to the other end of the arc of violence, it became voguish to view Clausewitz as a devotee of ‘total war’. Because he worked, fought and thought during the period of Napoleon’s wholly novel approach to warfare (in which the whole nation was harnessed, including its wealth, industry, population, politics, and armed forces, in the pursuit of ‘total war’), it was wrongly assumed that this was Clausewitz’s only aspiration. Some agreed with Liddell Hart, who held Clausewitz’s philosophy responsible for the carnage of the World Wars, but that was simply wrong.

Clausewitz makes it very clear that the ‘absolute’ nature of war is an ideal state which, in reality, happens only very rarely. He connects this idea with the subordination of war to policy, developing the theory that war reaches its most ‘pure’ form only when policy itself is hugely muscular, as it was in the wars following the French Revolution.  He never suggests that the total destruction of the enemy should be the ultimate goal of war: the goal of war is the implementation of policy, the muscularity of which can be ratcheted up or down at the direction of kings or politicians, not generals or admirals. This is what will determine the character of the war.

Now, for the first time since 1945, large-scale forces have been ranging across European soil and media commentators are reaching for the Clausewitzian lexicon. ‘Friction’ – the idea that in war even the simplest operations become more dangerous and slower – and the ‘moral component’ have become almost household phrases. For my money, though, the dual but related concepts of ‘interior lines’ and ‘culminating point’ have seldom been more clearly demonstrated than in recent events in Eastern Europe.

Simply put, as the numerically weaker Ukrainians fell back on familiar ground – their interior lines – and resupply became easier, they got stronger. As the more numerous Russians stretched further away from their bases with fuel, ammunition, air cover, and reinforcements getting harder to reach, and their lines of communication ever more vulnerable, they became weaker. Eventually, the apparently stronger force could go no further: they reached their culminating point and were ripe for counter-attack. Now that’s Clausewitz writ large.

Today, I foresee a renaissance for On War in military colleges around the world. Lord Raglan certainly had a copy of Clausewitz with him in the Crimea in 1854 (although I wonder if he opened it), and we know the German field marshal Erich von Manstein had a similar volume with him as he swept over the very same ground in the summer of 1942.

Now that this same span of country has become a cockpit once again, I have no doubt that professors and generals will be called in to draft explanatory essays. They will be asked to update Vom Kriege and to adapt it by explaining how the ‘moral dimension’ must now include the use of information and media, seeing both as just another warlike tool. While I’m sure the author would approve of anything that makes his work more easily understood by a modern audience, a little imagination and analysis will show that it’s all there already. I suspect, though, that any commander, in whatever conflict, who has a well-thumbed copy of this great work in his knapsack, will triumph. •

Images: Wikimedia Commons.