Published in 1832, re-published many times and translated into several languages, On War has been regarded by many as one of the greatest, if not the greatest book On War ever written.[i] Clausewitz’s interpretation of war as a continuation of politics – and, indeed, of society – has seen him called a ‘philosopher of war’.[ii] If this term is appropriate it is because he places war in its wider social and political context.[iii] But Clausewitz also provides concepts central to understanding the conduct of war. His theories of military strategy have received much attention, influencing many later theorists while also creating greater controversy.
Some political and military leaders have admired Clausewitz, believing that he offered an understanding of war that suited their purposes. In the years leading up to the Franco-Prussian War of 1870-71, for example, the Prussian general Count von Moltke thought that On War advocated Napoleonic-style warfare with an emphasis on mass, morale, patriotism and leadership. Prussia, Moltke concluded, must wage war vigorously and seek total victory.[iv]
Others have condemned Clausewitz for promoting such militarism. In 1908 Colonel F.N. Maude’s introduction to an English edition of On War declared that the spread of Clausewitz’s ideas were responsible for ‘the readiness for war of all European armies.[v] After WW I Captain Basil Liddell Hart echoed this view, depicting Clausewitz as ‘the apostle of total war’ and ‘the ill-omened prophet of mass’.[vi] After the outbreak of WW II Liddell Hart declared that On War and its theory of unlimited war ‘had gone far to wreck civilisation’.[vii]
Such extreme misrepresentations of Clausewitz did little to promote the understanding of war or the understanding of Clausewitz’s analysis of war.[viii] Fortunately, failure to grasp Clausewitz’s ideas has become less common and less influential in recent decades. This is partly because On War became more accessible to many scholars and military thinkers thanks to the Howard-Paret translation of 1976.[ix] Clausewitz has been paid serious academic attention and now boasts a long list of books and articles on his works as well as a scholarly website devoted to him.[x] War Colleges and military professionals now regularly salute him; academics and analysts frequently cite him.
The question of relevance
Before considering how some of Clausewitz’s ideas can be applied to the war in Ukraine, it is fair to ask whether ideas formulated around 200 years ago can be relevant to modern times. This is an issue Clausewitz himself recognised. His studies of earlier warfare almost totally excluded ancient and medieval campaigns because of their very different social, political and organisational circumstances. The absence of reliable sources was also a factor. [173-4] Clausewitz’s numerous campaign histories thus go back only as far as 1660 while On War itself refers almost exclusively to campaigns and battles from the Seven Years War (1756-63) onwards.
Surely the advent of industrialised warfare, nuclear weapons, ICBMs, global communications, cyber threats, remotely controlled weapons platforms, chemical and biological weapons and so on has changed everything about war? The doctrine of mutual assured destruction during the Cold War, for example, required the two superpowers to leave themselves vulnerable to attack – a concept unthinkable to Clausewitz.[xi] The world, however, has not seen an end to wars that display the essential, characteristics that Clausewitz identified. The war in Ukraine is being fought by sovereign states over competing national interests; it is being conducted primarily by organised armed forces under military command and political direction; and it is killing people and destroying assets. On War does not appear completely outdated.
Interestingly, some of Clausewitz’s own military histories bear on the question of relevance. In one such study he examines the campaigns conducted by Russia from bases in Ukraine (then part of Russia) against the Turks and Tatars in Crimea in the four summers from 1736 to 1739.[xii] On War mentions these campaigns briefly in a chapter entitled ‘The Key to the Country’ though mainly to debunk the idea that conquest of a particular stretch of territory will allow an attacker to dominate the defending country. [456-9] More relevant, as Alexander Burns points out, are Clausewitz’s observations on Russia’s conduct in these campaigns: Russia’s political purpose lacked clarity, vacillating between conquest of Crimea and simply weakening it by devastating its territory; Russia was initially overconfident of success; Russian logistics were poorly organised; and Russia accepted very heavy casualties in return for minor territorial gains. Burns also notes that, while the campaigns were ineffective, Russia learned lessons that stood it in good stead in subsequent wars.[xiii]
The relevance of Clausewitzian analysis to the war in Ukraine will be considered in relation to two of Clausewitz’s major strategic principles. The first is that defence is the stronger form of war, the second is that efforts need to be focused on an enemy’s centre of gravity. Both appear particularly relevant to the war in Ukraine but there are traps into which analysts may fall, especially if they seek to explain success or failure. One pitfall is to assume that following Clausewitz’s principles of strategy is a sure road to victory while failure to follow them leads to defeat. Another is the temptation to overlook the complexity and conditionality of Clausewitz’s strategic thinking. Warnings against such pitfalls abound in On War but they are not always heeded.
Defence is the stronger form of war
In examining the dynamic relationship between offence and defence in war Clausewitz weighs a wide range of factors. Some – for example, numbers and disposition of forces – are available to both attacker and defender but others favour one side or the other. Thus he
argues at several points in On War that ‘defense is a stronger form of fighting than the attack’. [84, 358, 380] He is not saying that defence will always triumph but that it possesses characteristics that make it more likely to prevail. By definition, defence has a passive aim – preservation – whereas offence has a positive goal, namely conquest. In short, it is simply ‘easier to hold ground than take it’. [357-8] Factors more readily available to the defence include fortifications, shorter supply lines and national morale. A defending state is also more likely to win support from allies.
Only one factor, Clausewitz argues, distinctly favours the offence, namely surprise. But this can effectively be achieved primarily at the tactical level. The surprise initiation of a war is far more difficult. Given the extensive preparations involved, Clausewitz suggests, war ‘will usually be announced in the press before a single shot is fired’.  Strategic surprise is highly valuable but usually requires ‘major, obvious and exceptional mistakes on the enemy’s part’. 
While friction troubles both defender and attacker there are dynamic factors that specifically burden the attack. First, as gains are made, they must be defended against counter-attacks. Resources must be devoted to defending these gains, often under less favourable conditions. Clausewitz describes the need to defend as the ‘mortal disease’ of the offence.  Second, the defending state may well be able to organise itself more effectively with shorter supply lines, use of militia forces and high morale. Third, the attacker loses momentum – thanks to factors such as casualties, supply problems, and delays caused by defensive strongpoints. Doubts in the political leadership may also arise or allies lose heart. [527, 567-9]
As a result, Clausewitz argues, there will be a ‘culminating point’ at which the burden becomes too great for the attack to carry.  A campaign must achieve its political purpose before reaching this point. Thus Napoleon, even though he had captured Moscow in 1812, fell victim to ‘strategic consumption, and had to use the last strength of his sick body to drag himself out of the country’.[xiv]
In many cases, however, the attack will not be pushed as far as its culminating point. Strength and ambition fade; pause, delay, and indecision take their place. Surprise is more difficult to achieve because energy is lacking. Inevitably, too, a general will have difficulty in recognising when the culminating point is approaching or even when it has been reached. Consequently, Clausewitz argues, most generals prefer caution for fear of overshooting the mark.  Only major political objectives and strong military leadership will drive the attack onwards.
As the attack becomes progressively weaker, moreover, there is a point at which the defence can take the initiative. For Clausewitz this means defence will cut less ‘sorry a figure when compared to attack’ which in turn ‘will no longer look so easy and infallible’.  It is when ‘the flashing sword of vengeance’ can be taken up and provide ‘the greatest moment for the defence’.  Indeed, Clausewitz never regards defence as purely passive since even when awaiting an assault ‘our bullets take the offensive’, while ‘a defensive campaign can be fought with offensive battles’. 
In putting forward the notion that defence is the stronger form of war Clausewitz is, of course, arguing in the abstract. He must assume there is no great disparity between the two sides in factors that may be critical to the success of otherwise of an attack. The number of troops, their morale and training, the deployment of forces, the achievement of strategic surprise, the strength of fortifications, the effectiveness of supply and logistics, popular support and the reactions of allies are all relevant to the actual outcome of a war. For the attack to triumph it must outperform its opponent in some or all of these dimensions. For the defence to succeed assets must be employed judiciously and energetically.
While Clausewitz implicitly and in places explicitly warns against expecting easy success in an attack, he does not present a case against aggression. The decision to initiate war is a matter for political leaders who must weigh expected benefits against uncertain risks. He does not condemn Napoleon for his disastrous invasion of Russia since this appeared the only possible way for France to avoid simultaneous wars against both East and West.  The furthest he goes is to describe Napoleon’s campaign as in a political sense ‘an extravaganza’. 
Ultimately it is a matter for politics – not for an analysis of war – to decide whether such great political risks and military efforts are justified. This is so even if they lead to national ruin. What he does caution is that political leaders should at least be clear about their objectives and understand the nature and possible consequences of any military action they undertake.
Centre of Gravity
A second concept sometimes called upon by those examining the war in the Ukraine is Clausewitz’s ‘centre of gravity’. Often this is taken to be an opponent’s capital city: capture Kyiv (or Moscow, or wherever) and surrender will follow. Alternatively, it may be taken to mean a point of weakness such as an enemy’s communications, morale, or a gap in defences which should therefore be the principal target of the attack.
Clausewitz’s analysis is more subtle. He borrows the term ‘centre of gravity’ [Schwerpunkt] from mechanics – the imagined point where all the forces of gravity bear on an object, a point which if moved can throw that object off balance. For Clausewitz the centre of gravity in strategy is not the enemy’s point of strength or weakness but his point of unity and cohesion. Especially where a war is fought to achieve a decisive result rather than a minor advantage, the centre of gravity is ‘the most effective target for a blow’. [485-6]
Identifying the centre of gravity of an opponent in a particular conflict is ‘a major act of strategic judgement’.  And it is all the more difficult given incomplete and perhaps inaccurate intelligence about the opponent and the inherent unpredictability of war. In the course of a war, moreover, the centre of gravity may change as hostilities impact on both belligerents and cause ambitions to change. Clausewitz suggests four candidates where an enemy’s centre of gravity can be located: its territory, its capital city, its alliances and its army.
Territory is important because it holds people and resources which, once captured, are lost to the defending nation. But they do not add automatically to the strength of the conqueror since popular resistance may be provoked and harnessing the resources gained may require significant effort. In a major war, Clausewitz suggests, territory may not be that important. Occupation by the enemy may be only temporary such that territory is ‘merely lent to him’. 
A capital city may seem the most obvious candidate for a centre of gravity. As Clausewitz observes, it is the centre of a nation’s political activity and administration, and often represents its will to resist. But Napoleon’s occupation of Moscow proved that a capital is not always decisive in ending a war.[xv] Putin’s initial thrust toward Kyiv suggests his belief that Ukraine’s capital was the centre of gravity and hence the key to success.
In some wars a nation’s principal ally may serve as the centre of gravity so the ally’s centre of gravity must be considered the focus of attack. The task is easier, Clausewitz argues, where there are several allies on which a state depends. For their unity depends on mutual political interests which may be ‘precarious and imperfect’ and on their cohesion in action which will ‘usually be very loose, and often completely fictitious’.  The attacker, Clausewitz suggests, can exploit division among allies of the defender directly or chip away at their unity step by step. The war in Ukraine may prove an interesting test case.
The most common centre of gravity is the opponent’s armed forces. In symbolic terms defeat of an enemy army is often more effective than occupying enemy territory or its capital. Napoleon’s problem before Moscow was that his army was too weak to defeat the Russian army.  Occupation of the city had little effect on the course of the war. The loss of an army, by contrast, usually undermines an opponent’s will to resist and exposes its people to occupation. Even so, in Clausewitz’s view, military defeat may be countered by a resort to militia (reserve) or irregular forces which can offer a chance of successful defence. [479-83]
Ukraine and strategic theory
That the war is a continuation of political intercourse with the addition of other means goes without saying. More complex is its relationship with strategic theory. For Clausewitz strategic theory is derived from a study of actual military history through a process he calls Kritik (critical analysis).[xvi] The result is initially an understanding of past wars – not necessarily of present or future wars. It is not ‘a new technique’ for waging war but provides ‘a rationale for the actions of every general in history’.  When it comes to application to current or future wars Clausewitz is clear that strategic theory has limitations.
First, every war has its unique circumstances, even those wars that occur in the same era or locations, or among the same belligerents. Strategy is a matter of successive actions and reactions, many of them unpredictable, such that wars can take on more variations than a game of chess.
Second, success in war is not a matter of applying this or that strategic theory; nor will ignoring one or another theory inevitably result in failure. Strategic theory helps the general or statesman learn from the past and guides their decisions. It does not offer a sure recipe for success. For principles of strategy are applied during the course of a war when information is far from complete or reliable and when hindsight is unavailable. Military leaders will use their knowledge, experience and judgement, but must to some extent ‘guess’ how events will turn out. 
Generals are in essence gamblers. The best display of what Clausewitz calls military ‘genius’ – a combination of not simply knowledge and intellect but also strong character, quickness of perception (coup d’oeil), boldness and perseverance. [100-112] The height of genius is to grasp which principles of strategy are relevant in any given situation (and which can be ignored) and then to apply them effectively. And, one might add, to change strategies if events demand it.
Third, when concepts such as centres of gravity or defence as the stronger form of warfare are used, it is important to recognise their interdependence with the actual course of the war. President Putin, for example, may well have ignored Clausewitz’s ‘advice’ that defence is the stronger form of warfare by underestimating Ukrainian resistance and overestimating Russian strength. But no one could be sure in advance that such a misjudgement would be critical in the war.
Against a less popular leader than Zelensky and with better planning and logistics the first clash of arms might have led to the collapse of Ukrainian forces, the fall of Kyiv and Ukraine’s acceptance of defeat. As Clausewitz recognises, it is important to estimate the enemy’s strength and will to resist, but immediately adds that it cannot be known ‘whether the first shock of battle will steel the enemy’s resolve and stiffen his resistance, or whether, like a Bologna flask, it will shatter as soon as its surface is scratched’. 
In conclusion, it is important not to see success or failure in war as proof of the validity or invalidity of any given theory – evidence, perhaps, but not proof. Clausewitz’s analysis of war is valuable in understanding the strategy – and to some extent the politics – of the war in Ukraine. But it is not a formula for winning wars – that requires the far more complex and difficult effort of bringing resources to bear on an opponent in accord with strategies judged to be relevant. Clausewitz wrote a brilliant analysis of strategy and its characteristics, not a handbook for waging wars.
[i] See, for example, Bernard Brodie, ‘On Clausewitz: A Passion for War’, World Politics, vol. 75 no. 2 (January 1973).
[ii] W.B. Gallie, Philosophers of Peace and War: Kant, Clausewitz, Marx, Engels and Tolstoy (Cambridge, Cambridge University Press, 1978); Raymond Aron, Clausewitz: Philosopher of War, trans. C. Booker, N. Stone (London: Routledge, Kegan Paul, 1983). See also Hugh Smith, ‘Clausewitz as Sociologist’, Infinity Journal, Special Edition, Clausewitz and Contemporary Conflict (February 2012). https://www.infinityjournal.com/article/47/Clausewitz_as_Sociologist/
[iii] Hugh Smith, On Clausewitz: A Study of Military and Political Ideas (Basingstoke: Palgrave Macmillan, 2005) passim.
[iv] Brian Bond, The Pursuit of Victory (Oxford: Clarendon Press,1998) 78.
[v] Carl von Clausewitz, On War, trans. J.J. Graham (London: Kegan Paul, new rev ed. 1940) ix.
[vi] Brian Bond, Liddell Hart: A Study of his Military Thought (London: Cassell, 1977) 37-8, 80-81.
[vii] Basil Liddell Hart, Strategy: The Indirect Approach (London: Faber & Faber, 3rd rev. ed. 1954) 357.
[viii] On interpretations of Clausewitz in the English-speaking world see Christopher Bassford, Clausewitz in English: The Reception of Clausewitz in Britain and America 1815-1945 (New York: Oxford University Press, 1994).
[ix] Carl von Clausewitz, On War, trans. and edited by Michael Howard & Peter Paret (Princeton: Princeton University Press, 1976). Subsequent citations are from this edition with page numbers in square brackets.
[x] https://www.clausewitzstudies.org There is also a more broadly focused website https://www.clausewitz.com
[xi] Smith, On Clausewitz, 244-8.
[xii] Entitled ‘Krieg der Russen gegen die Türken von 1736–1739’ the study is short (12 pages) and not yet translated into English. Accessed at https://play.google.com/books/reader?id=p55DAAAAcAAJ&pg=GBS.PA16&num=19
[xiii] Alexander S. Burns, ‘Clausewitz’s Analysis Resonates to this Day’, The National Interest, 1 March 2023.
[xiv] Carl von Clausewitz, The Campaign of 1812 in Russia (London: 1843; reprinted by Academic International, Hattiesburg, 1970), 166.
[xv] Clausewitz refers to Moscow as the effective capital of Russia while recognising St Petersburg, the formal capital, as a ‘second capital’. This duality complicated Russia’s defensive strategy. 
[xvi] On War, Book II, ch. 5; on the relationship between theory and practice in Clausewitz’s thinking see Smith, On Clausewitz, chs 14,15.