The enthusiastic approval of Adolf Hitler is scarcely the kind of endorsement most authors would want, and the writings of the Prussian military theorist Carl von Clausewitz (1780–1831) certainly had that. His On War was on the list of the top one hundred wholesome titles booksellers in Nazi Germany were supposed to carry. Hailing Clausewitz as the prophet of Absolute War, the Nazi warlord would pore over him at night in the study of the Berghof in the Bavarian Alps with its sign ordering ABSOLUTE SILENCE. He would quote him endlessly at his generals, and, when things started to come apart, Hitler used Clausewitz “as a sort of spiritual talisman,” in the words of the historian Peter Baldwin. Finally, in his political testament, Hitler urged his countrymen to keep on fighting, “true to the creed of the great Clausewitz.”

After the war, an understandable Clausewitz fatigue set in: the German general Gunther Blumentritt stated that letting the military read On War was like “allowing a child to play with a razor blade.” And to this day, many Germans still regard Clausewitz as tainted.

But as Donald Stoker makes clear in Clausewitz: His Life and Work, Hitler had no exclusive ownership claims on Clausewitz.1 Having distilled the essence of war, devoid of moral considerations, Clausewitz is an equal opportunity theorist: dictatorships and democracies alike have found his insights useful. Lenin thought so, and so did Mao.

Colonel Harry Summers’s On Strategy channeled him to explain what went wrong in Vietnam. With its preconditions for going to war—a clear idea of what one wishes to achieve, the support of the people, and the use of overwhelming force—the Weinberger doctrine built on Clausewitz. And though he has repeatedly been pronounced irrelevant or outdated—with regard to nuclear war or in war involving non-state actors, On War always pops back up again, most recently in an al Qaeda safe house in Afghanistan with the passages on courage underlined.

Nobody ever accused On War of being an easy read—in certain passages you can feel your lips move—but by presenting Clausewitz’s career as a professional soldier and his theoretical writings as inextricably linked, Stoker has lightened the task considerably. Clausewitz experienced war from the sharp end of the stick, participating in some three dozen battles, and Stoker deftly demonstrates how he develops the ideas that end up in On War. He also points out some of the book’s contradictions that have caused otherwise sensible men to reach wildly differing conclusions.

Born in 1780 in the town of Burg in Prussia, Clausewitz was the son of a junior officer in the Prussian army. As was not uncommon at the time, he entered the army at the age of eleven: “I am a son of the camp,” he wrote. He got his baptism by fire in 1793 against French revolutionary forces on the Rhine in the siege of Mainz and in the clashes in the Vosges wilderness, where his two fellow ensigns perished. The following year he saw further action, including “a fierce fight in a bad position from which I luckily escaped.”

What Europe’s monarchies were up against was a new kind of warfare. Up until then, its rulers all kept small professional armies as their expensive toys. The troops looked smart on the parade ground, performing their military minuets, but were far too precious to lose in war, so much energy was spent on maneuvering, on avoiding battle rather than fighting it.

The French Revolution had created a different kind of army, an army based on mass conscription, making France a nation under arms. Not yet capable of fancy moves on the battlefield, the French instead attacked in dense columns, carried forward by ideological zeal. “War untrammeled by any conventional restraints had broken loose in all its elemental fury,” writes Clausewitz.

Lucky to be in one piece, Clausewitz, now a junior lieutenant, returned to a garrison in Neuruppin. His regimental commander believed in education, and his tutor, Major von Sydow, “distinguished between raw and educated courage”—a theme, notes Stoker, that was to resurface in the section on military genius in On War. A keen student, Clausewitz was sent to Berlin’s General Military College where he graduated first in his class. He called Scharnhorst, the school’s superintendent, “the father and friend of my spirit.”

Among Clausewitz’s reading, in addition to the philosophers of the Enlightenment, Stoker lists Machiavelli, Tempelhoff, Maurice de Saxe, Frederick the Great, and Turenne. Not content to study others, in 1804 he set to work on a manuscript of his own, the extant draft of which bears the title Strategie. In a review he dismissed his contemporary Dietrich Heinrich von Bülow’s Spirit of the Modern System of War, which reduces war to a geometric formula, as “the children’s military companion.”

To Clausewitz, war’s many intangibles made it an art, not a science. Others got lost in the minutiae of how to construct fortresses or design weapons: “All this is in relation to fighting not much different from the task of the sword cleaner to the art of fencing,” he wrote. What Clausewitz wanted, says Stoker, was a philosophical debate about the nature of war with a set of clearly defined terms as its basis.

After the fall of Robespierre, the Prussians made an agreement with France that kept them out of war for eleven years. But while the Prussian army was going to pot in Potsdam, Napoleon was turning the French army into an ever more effective instrument of his will, as proved by his victories at Marengo and Austerlitz.

Becoming adjutant to Prince August von Preussen in 1803 gave Clausewitz a chance to observe his country’s elite close up, including its ruler Frederick William III whom he deemed “too full of the old Nordic sense of doubt.” Prodded by Queen Louise, whom Napoleon considered “the only real man in Europe,” Frederick finally sided with Russia in 1806 against the French—unfortunately without waiting for the Russians to be in place to assist him.

As a result, Clausewitz saddled up for his second war where he caught the full blast of Napoleonic warfare. The battles of Jena and Auerstedt were catastrophes for the Prussians, and for good reasons: as Stoker notes, Prussia’s hopeless command structure involved “three field commanders, and two quartermasters general, where she should only have one of each.”

Describing the obstruction Scharnhorst faced as Quartermaster General, Clausewitz employs the term “friction” for the first time. Though he knew of no man “more capable of overcoming difficulties” than Scharnhorst, his mentor was “paralyzed by the unceasing friction of other opinions.” This he later expanded to include every unpredictable factor such as the weather, troop morale, and, not least, the reactions of the enemy, that makes war such a tricky business.

At Jena, Napoleon hit the smaller of the Prussian forces with panic ensuing, and at Auerstadt, where Clausewitz fought, the Prussian main body was defeated by Louis-Nicolas Davout, despite having had a two-to-one advantage. Unlike at Jena, however, there was no panic: the troops began a two-week fighting retreat on paltry rations until the prince and Clausewitz finally surrendered at Prenzlau. Which, for the two of them, meant having to go to France as prisoners of war.

Their imprisonment, however, did not involve Andersonville-type horrors or a British prison hulk, says Stoker, but a rather comfortable existence in a small village outside Paris, with visits to the capital. But except for Madame de Staël, whose salon he visited in Switzerland, Clausewitz despised anything French: The society beauty Madame Récamier, whom David had painted elegantly reclining on her chaise longue, Clausewitz has down as “a very common flirt.”

Having taken Berlin, Napoleon’s next target was the Russians: Eylau was a draw, but he won decisively at Friedland, which made Czar Alexander throw in his hand for the time being. After Napoleon and Alexander’s meeting on the barge on the Niemen river in June 1807, Frederick had to swallow the Treaty of Tilsit, which cost him half his land, and an additional agreement that limited his army to 42,000 men and nixed militias and subscription.

On his return from captivity in 1808, Clausewitz got involved in the reform commission in which August Niedhart von Gneisenau, who became his second mentor, was a prominent member. Romanticism was strong in Prussia: “The Enlightenment was seen as an occupier’s alien culture,” notes Stoker, “one lacking a soul and a distinctive Germanness.” Such feelings of patriotism needed to be encouraged, the commission believed, by abolishing serfdom and by breaking the Junker monopoly on the officer corps by emphasizing merit.

The reformers thus favored joining Austria in its call for an all-German war against Napoleon in 1809, but the King wasn’t buying: “A political existence of some kind, no matter how small it be, is better than none.” In this case probably wisely, notes Stoker, since Russia stayed out. The Austrians were duly trounced at Wagram.

At Berlin’s General War School, Clausewitz taught tactics—“My pursuits are almost as peaceful as planting cabbages”—before being promoted to general staff officer in 1810. In notes from these years, Stoker finds him introducing the two elements of passion and chance—here known as “luck”—to which he later added a third element, politics, to make up On War’s “Wondrous Trinity”: that unstable mix of primitive violence, creativity, and rationality, associated with, respectively, the people, the commander, and the government, which characterizes warfare.

With a clash between France and Russia becoming ever more likely, Clausewitz and Gneisenau advocated a “people’s war” against the French along the lines of Spain. The notion did not sit well with Frederick: in the margin of Gneisenau’s policy recommendation, he scribbled “Nobody would come!” and “good—as poetry!” Instead, caving in to French pressure, the King threw in his lot with Napoleon in 1812. In disgust, Clausewitz resigned his commission and joined the Russian army.

Initially assigned to the “distinguished idlers” at the Russian headquarters, he describes himself as feeling “so utterly useless that he would rather have served as a subaltern in the line.” For a while, he got himself assigned to the rearguard, but was soon returned to staff, a sensible move, notes Stoker, since he did not speak a word of Russian and couldn’t make himself understood by his troops—“a deaf mute,” he calls himself.

Clausewitz was present at both Smolensk and Borodino, after which the Russians resumed their retreat in keeping with their defensive strategy of sucking the enemy in deeper and deeper. His was one of the last units to pass through a burning Moscow. He drinks “from the filthiest puddles,” has three hollow teeth, and his hands look like “yellow leather.” When the fortunes are reversed, and it is the French who do the retreating, he witnesses the Grande Armée’s disastrous crossing of the Berezina river.

But Clausewitz’s most important contribution came, says Stoker, when his unit made contact with the Prussian expeditionary force of 14,000 men under General Yorck, fighting for the French. He managed to persuade the general to take his troops out of the fighting. What makes the so-called Tauroggen agreement, which Clausewitz drafted, such a significant event in the Napoleonic wars, says Stoker, was that it shifted the alliance structure. Prussia was no longer to be found in Napoleon’s column.

From a start of 300,000 men, by the end of the Russian adventure, Napoleon’s army had been reduced to less than 20,000, much as Clausewitz had predicted, but Napoleon retained his ability to raise new armies. In the campaigns of 1813–1814, which led to Napoleon’s first fall, we find Clausewitz detailed to Blücher’s Silesian army as a Russian liaison officer. Frederick hadn’t forgiven him for his Russian adventure.

Clausewitz took part in the battles of Lutzen and Bautzen: at the former, the entire staff fought hand to hand—Scharnhorst died from his wounds soon after. In a cavalry charge, Clausewitz was himself hit behind the ear by an infantry bayonet. The Prussians lost narrowly on both occasions, but no longer considered “a lost battle a lost war,” says Stoker, a resilience resulting from their reform efforts. “These animals have learned something,” was Napoleon’s grudging compliment.

After a short armistice, Austria joined the lineup against Napoleon which now counted all the major European nations. The Battle of Leipzig of October 16, 1813 finished Napoleon’s hopes in Germany and set the stage for the 1814 allied invasion of France itself. Here, using his advantage of interior lines, Napoleon still had nifty moves left—in On War, Stoker reminds us, Clausewitz does not buy the idea that Napoleon’s abilities had diminished—but the odds were just too unfavorable, even for him: Paris surrendered and Napoleon abdicated.

But to Clausewitz, the campaigns of 1813–1814 were disappointing, as he spent them on the fringes, first posted in Northern Germany in the Russo-German legion and subsequently in Belgium and the Netherlands, forever grousing about Frederick’s refusal to let him back into the Prussian army.

Napoleon’s return from Elba gave Clausewitz one more shot at glory. Finally reinstated in the Prussian army as a staff colonel, he fought at Ligny, where the Prussians were mauled by Marshall Grouchy. They regrouped at Wavre, and the rearguard, in which Clausewitz once more found himself, managed to keep Grouchy at bay. By doing so, they allowed Blücher to come to Wellington’s aid at Waterloo.

Clausewitz called the night of the sixteenth of June on the road to Wavre the worst night of his life: “I believe my hair turned gray that night.” But the Prussian army had again proved its mettle. In Clausewitz’s later study of the 1815 campaign, Stoker traces many of the key notions found in On War: center of gravity, military genius, rational calculation.

In 1816, Clausewitz began writing On War and two years later he became the head of the War College, an exclusively administrative post with the rank of Generalmajor. By this time, the King had had it with reform, says Stoker, and Clausewitz acquiesced. But his job left him plenty of time for writing and for correspondence, among which Stoker highlights a letter to Major von Roeder on the general staff, which contains what became the central idea of On War: “War is not an independent phenomenon,” Clausewitz writes, “but the continuation of politics by different means.” Consequently, he goes on, “the main lines of every major strategic plan are thoroughly political in nature, and their political character increases the more the plan encompasses the entire war and the entire state.” What is special about this, says Stoker, is not so much the “war as an instrument of politics” part—others had pointed that out: Machiavelli, for one, Took it for granted—but Clausewitz’s insight that politics permeates war at all levels.

But he still had military ambitions. In 1830, about to take up a position with the artillery in Breslau, he boxes up his writings, including the On War manuscript, each having its neat label. On War is a mess. Stoker cites an earlier note: “The first chapter in book one alone I regard as finished,” Clausewitz writes. “Should an early death interrupt my work, what is here will of course only deserve to be called a shapeless mass of thoughts—subject to endless misunderstanding.”

He never got further with it. Having joined Gneisenau in 1832 as his chief of staff in an army of observation in Posen, monitoring the Polish revolt, he was charged with containing an outbreak of cholera. His efforts failed, claiming first Gneisenau, and then, a few months later, himself in his home in Breslau. It was therefore left to his widow, Marie, to prepare his writings for publication. With an 1832 first edition of only 1,500 copies, some of which still remained unsold when the second edition was published in 1857, On War was no gold mine. But when the architect of the Prussian victory over the French in 1870–71, Helmuth von Molkte, pronounced Clausewitz the biggest thing since Homer and the Bible, he became required reading for Prussian officers, while the French started studying him to figure out what the blazes had hit them.

Seen on his own terms, notes Stoker, his career was a failure: he never “did scale the highest peak,” in the words of his wife. He never commanded an army. But in terms of the durability of On War, he has been a tremendous success.

This durability derives from the fact that though there are sections devoted to tactics and therefore outdated, Clausewitz did not intend On War as a manual, but more as a training ground for judgment: theory, he wrote, “is meant to educate the mind of the future commander, or, more accurately, to guide him in his self-education, not to accompany him to the battlefield.”

The book is unflinching in its acceptance of war’s horrors: “Kind-hearted people of course think that there was some ingenious way to disarm or defeat an enemy without too much bloodshed and might imagine that is the true goal of war. Pleasant as it sounds, that is a fallacy.”

To function in war’s highly unstable universe, judgment, intuition, and fortitude of the highest order is called for, a mind that “even in the darkest hour retains some glimmerings of the inner light which leads first to truth and second the courage to follow this faint light wherever it may lead.” Scharnhorst had it, as did Gneisenau, and few could beat Blücher for steadiness—and never mind that the good marshal believed himself to have been impregnated by an elephant.

Napoleon, of course, was in a class all by himself. Though despising the man’s politics, Clausewitz calls him “the God of War,” and “the most determined general the world has ever seen.” But Napoleon’s fault, he suggests, was that he fell in love with it, waging war for the hell of it.

As for the contradictions and misinterpretations, says Stoker, many can be ascribed to the unfinished character of the work, notably the concept of “absolute war”: Thus at one point, Clausewitz has “absolute war” down as something Napoleon has perfected, and that he himself had been singed by, while a little later he says that “absolute war has never in fact been achieved.”

This confusion led the British military analyst Basil Liddell Hart to call Clausewitz “the evil genius of military thought,” and hold him responsible for the mass slaughter of World War I, while John Keegan blames him for Hitler’s savagery. Stoker does not agree: “He does not use ‘total war’ in the modern sense.” Rather, Stoker cites those who view the idea as being more akin to Kant’s “pure reason” or Newton’s “frictionless world,” an abstract construct. In such a world, “nothing inhibits the struggle,” writes Stoker. “But in reality, many things do.”

Besides, as Beatrice Heuser points out in Reading Clausewitz, in the period leading up to World War I, military experts all across Europe were busy rejecting Clausewitz’s views on the strength of the defensive, instead worshipping the offensive, only to see their arguments mowed down by machine gun.

Regarding Hitler, Clausewitz would scarcely recommend allowing one’s country to be turned into an ash heap. Like so many others when reading Clausewitz, the German dictator was looking for confirmation of already held beliefs, for certainties. In Clausewitz’s universe, as Stoker demonstrates so well, there are none. Clausewitz does not give the answers, but he teaches you to pose the questions.

1 Clausewitz: His Life and Work, by Donald Stoker; Oxford University Press, 376 pages, $27.95.