Front Page Titles (by Subject) CHAPTER XXI: INVASION - On War, vol. 3
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CHAPTER XXI: INVASION - Carl von Clausewitz, On War, vol. 3 
On War, trans. Col. J.J. Graham. New and Revised edition with Introduction and Notes by Col. F.N. Maude, in Three Volumes (London: Kegan Paul, Trench, Trubner & C., 1918). Vol. 3.
Part of: On War
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Almost all that we have to say on this subject consists in an explanation of the term. We find the expression very frequently used by modern authors and also that they pretend to denote by it something particular. Guerre d’invasion occurs perpetually in French authors. They use it as a term for every attack which enters deep into the enemy’s country, and perhaps sometimes mean to apply it as the antithesis to methodical attack, that is, one which only nibbles at the frontier. But this is a very unphilosophical confusion of language. Whether an attack is to be confined to the frontier or to be carried into the heart of the country, whether it shall make the seizure of the enemy’s strong places the chief object, or seek out the core of the enemy’s power, and pursue it unremittingly, is the result of circumstances, and not dependent on a system. In some cases, to push forward may be more methodical, and at the same time more prudent than to tarry on the frontier, but in most cases it is nothing else than just the fortunate result of a vigorous attack, and consequently does not differ from it in any respect.
ON THE CULMINATING POINT OF VICTORY*
The conqueror in a War is not always in a condition to subdue his adversary completely. Often, in fact almost universally, there is a culminating point of victory. Experience shows this sufficiently; but as the subject is one especially important for the theory of War, and the pivot of almost all plans of campaigns, while, at the same time, on its surface some apparent contradictions glitter, as in ever-changing colours, we therefore wish to examine it more closely, and look for its essential causes.
Victory, as a rule, springs from a preponderance of the sum of all the physical and moral powers combined; undoubtedly it increases this preponderance, or it would not be sought for and purchased at a great sacrifice. Victory itself does this unquestionably; also its consequences have the same effect, but not to the utmost point—generally only up to a certain point. This point may be very near at hand, and is sometimes so near that the whole of the results of a victorious battle are confined to an increase of the moral superiority. How this comes about we have now to examine.
In the progress of action in War, the combatant force is incessantly meeting with elements which strengthen it, and others which weaken it. Hence it is a question of superiority on one side or the other. As every diminution of power on one side is to be regarded as an increase on the opposite, it follows, of course, that this double current, this ebb and flow, takes place whether troops are advancing or retiring.
It is therefore necessary to find out the principal cause of this alteration in the one case to determine the other along with it.
In advancing, the most important causes of the increase of strength which the assailant gains, are:
(1) The loss which the enemy’s Army suffers, because it is usually greater than that of the assailant.
(2) The loss which the enemy suffers in inert military means, such as magazines, depôts, bridges, &c., and which the assailant does not share with him.
(3) That from the moment the assailant enters the enemy’s territory, there is a loss of provinces to the defence, consequently of the sources of new military forces.
(4) That the advancing Army gains a portion of those resources, in other words, gains the advantage of living at the expense of the enemy.
(5) The loss of internal organisation and of the regular action of everything on the side of the enemy.
(6) That the Allies of the enemy secede from him, and others join the conqueror.
(7) Lastly, the discouragement of the enemy who lets the arms, in some measure, drop out of his hands.
The causes of decrease of strength in an Army advancing, are:
(1) That it is compelled to lay siege to the enemy’s fortresses, to blockade them or observe them; or that the enemy, who did the same before the victory, in his retreat draws in these troops to his main body.
(2) That from the moment the assailant enters the enemy’s territory, the nature of the theatre of war is changed; it becomes hostile; we must occupy it, for we cannot call any portion our own beyond what is in actual occupation and yet it everywhere presents difficulties to the whole machine which must necessarily tend to weaken its effects.
(3) That we are removing further away from our resources, whilst the enemy is drawing nearer to his; this causes a delay in the replacement of expended power.
(4) That the danger which threatens the State, rouses other powers to its protection.
(5) Lastly, the greater efforts of the adversary, in consequence of the increased danger; on the other hand, a relaxation of effort on the side of the victorious State.
All these advantages and disadvantages can exist together, meet each other in a certain measure, and pursue their way in opposite directions, except that the last meet as real opposites, cannot pass, therefore mutually exclude each other. This alone shows how infinitely different may be the effect of a victory according as it stuns the vanquished or stimulates him to greater exertions.
We shall now try to characterise, in a few words, each of these points singly.
(1) The loss of the enemy when defeated may be at the greatest in the first moment of defeat, and then daily diminish in amount until it arrives at a point where the balance is restored as regards our force; but it may go on increasing every day in an ascending ratio. The difference of situation and relations determines this. We can only say that, in general, with a good Army the first will be the case, with an indifferent Army the second; next to the spirit of the troops, the spirit of the Government is here the most important thing. It is of great consequence in War to distinguish between the two cases in practice, in order not to stop just at the point where we ought to begin in good earnest, and vice versâ.
(2) The loss which the enemy sustains in that part of the apparatus of War which is inert, may ebb and flow just in the same manner, and this will depend on the accidental position and nature of the depôts from which supplies are drawn. This subject, however, in the present day, cannot be compared with the others in point of importance.
(3) The third advantage must necessarily increase as the Army advances; indeed, it may be said that it does not come into consideration until an Army has penetrated far into the enemy’s country; that is to say, until a third or a fourth of the country has been left in rear. In addition, the intrinsic value which a province has in connection with the War comes also into consideration.
In the same way the fourth advantage should increase with the advance.
But with respect to these two last, it is also to be observed that their influence on the combatant powers actually engaged in the struggle is seldom felt so immediately; they only work slowly and by a circuitous course; therefore we should not bend the bow too much on their account, that is to say, not place ourselves in any dangerous position.
The fifth advantage, again, only comes into consideration if we have made a considerable advance, and if by the form of the enemy’s country some provinces can be detached from the principal mass, as these, like limbs compressed by ligatures, usually soon die off.
As to six and seven, it is at least probable that they increase with the advance; furthermore, we shall return to them hereafter. Let us now pass on to the causes of weakness.
(1) The besieging, blockade, and investment of fortresses generally increase as the Army advances. This weakening influence alone acts so powerfully on the condition of the combatant force, that it may soon outweigh all the advantages gained. No doubt, in modern times, a system has been introduced of blockading places with a small number of troops, or of watching them with a still smaller number; and also the enemy must keep garrisons in them. Nevertheless, they remain a great element of security. The garrisons consist very often in half of people, who have taken no part in the War previously. Before those places which are situated near the line of communication, it is necessary for the assailant to leave a force at least double the strength of the garrison; and if it is desirable to lay formal siege to, or to starve out, one single considerable place, a small Army is required for the purpose.
(2) The second cause, the taking up a theatre of War in the enemy’s country, increases necessarily with the advance, and if it does not further weaken the condition of the combatant force at the moment, it does so at all events in the long run.
We can only regard as our theatre of War, so much of the enemy’s country as we actually possess; that is to say, where we either have small bodies in the field, or where we have left here and there strong garrisons in large towns, or stations along the roads, &c.; now however small the garrisons may be which are detached, still they weaken the combatant force considerably. But this is the smallest evil.
Every Army has strategic flanks, that is, the country which borders both sides of its lines of communications; the weakness of these parts is not sensibly felt as long as the enemy is similarly situated with respect to his. But that can only be the case as long as we are in our own country; as soon as we get into the enemy’s country, the weakness of these parts is felt very much, because the smallest enterprise promises some result when directed against a long line only feebly, or not all, covered; and these attacks may be made from any quarter in an enemy’s country.
The further we advance, the longer these flanks become, and the danger arising from them is enhanced in an increased ratio, for not only are they difficult to cover, but the spirit of enterprise is also first roused in the enemy, chiefly by long insecure lines of communication, and the consequences which their loss may entail in case of a retreat are matter of grave consideration.
All this contributes to place a fresh load on an advancing Army at every step of its progress; so that if it has not commenced with a more than ordinary superiority, it will feel itself always more and more cramped in its plans, gradually weakened in its impulsive force, and at last in a state of uncertainty and anxiety as to its situation.
(3) The third cause, the distance from the source from which the incessantly diminishing combatant force is to be just as incessantly filled up, increases with the advance. A conquering Army is like the light of a lamp in this respect; the more the oil which feeds it sinks in the reservoir and recedes from the focus of light, the smaller the light becomes, until at length it is quite extinguished.
The richness of the conquered provinces may certainly diminish this evil very much, but can never entirely remove it, because there are always a number of things which can only be supplied to the troops from their own country—men in particular; because the subsidies furnished by the enemy’s country are, in most cases, neither so promptly nor so surely forthcoming as in our own country; because the means of meeting any unexpected requirement cannot be so quickly procured; because misunderstandings and mistakes of all kinds cannot so soon be discovered and remedied.
If a Prince does not lead his Army in person, as became the custom in the last Wars, if he is not anywhere near it, then another and very great inconvenience arises in the loss of time occasioned by communications backwards and forwards; for the fullest powers conferred on a Commander of an Army are never sufficient to meet every case in the wide expanse of his activity.
(4) The change in political alliances. If these changes, produced by a victory, should be such as are disadvantageous to the conqueror, they will probably be so in a direct relation to his progress, just as is the case if they are of an advantageous nature. This all depends on the existing political alliances, interests, customs, and tendencies, on princes, ministers, &c. In general we can only say that when a great State which has smaller Allies is conquered, these usually secede very soon from their alliance, so that the victor, in this respect, becomes stronger with every blow; but if the conquered State is small, protectors much sooner present themselves when his very existence is threatened, and others, who have helped to place him in his present embarrassment, will turn round to prevent his complete downfall.
(5) The increased resistance on the part of the enemy which is called forth. Sometimes the enemy drops his weapon out of his hands from terror and stupefaction; sometimes an enthusiastic paroxysm seizes him, every one runs to arms, and the resistance is much stronger after the first defeat than it was before. The character of the people and of the Government, the nature of the country and its political alliances, are here the data from which the probable effect must be conjectured.
What countless differences these two last points alone make in the plans which may and should be made in War in one case and another. Whilst one, through an excess of caution, and what is called methodical proceedings, fritters away his good fortune, another, from a want of rational reflection, tumbles into destruction.
In addition, we must here call to mind the supineness which not unfrequently comes over the victorious side when danger is removed; whilst, on the contrary, renewed efforts are then required in order to follow up the success. If we cast a general glance over these different and antagonistic principles, the deduction doubtless is, that the profitable use of the onward march in a War of aggression, in the generality of cases, diminishes the preponderance with which the assailant set out, or which has been gained by victory.
Here the question must naturally strike us: If this be so, what is it which impels the conqueror to follow up the career of victory to continue the offensive? And can this really be called making further use of the victory? Would it not be better to stop where as yet there is hardly any diminution of the preponderance gained?
To this we must naturally answer: the preponderance of combatant forces is only the means, not the end. The end, or object, is to subdue the enemy or at least to take from him part of his territory, in order thus to put ourselves in a condition to realise the value of the advantages we have gained when we conclude a peace. Even if our aim is to conquer the enemy completely, we must be content that, perhaps, every step we advance, reduces our preponderance, but it does not necessarily follow from this that it will be nil before the fall of the enemy; the fall of the enemy may take place before that, and if it is to be obtained by the last minimum of preponderance, it would be an error not to expend it for that purpose.
The preponderance which we have or acquire in War is, therefore, the means, not the end, and it must be staked to gain the latter. But it is necessary to know how far it will reach, in order not to go beyond that point, and instead of fresh advantages, to reap disaster.
It is not necessary to introduce special examples from experience in order to prove that this is the way in which the strategic preponderance exhausts itself in the strategic attack; it is rather the multitude of instances which has forced us to investigate the causes of it. It is only since the appearance of Buonaparte that we have known campaigns between civilised nations, in which the preponderance has led, without interruption, to the fall of the enemy; before his time, every campaign ended with the victorious Army seeking to win a point where it could simply maintain itself in a state of equilibrium. At this point, the movement of victory stopped, even if a retreat did not become necessary. Now, this culminating point of victory will also appear in the future, in all Wars in which the overthrow of the enemy is not the military object of the War; and the generality of Wars will still be of this kind. The natural aim of all single plans of campaigns is the point at which the offensive changes into the defensive.
But now, to overstep this point is more than simply a useless expenditure of power, yielding no further result, it is a destructive step which causes reaction; and this reaction is, according to all general experience, productive of most disproportionate effects. This last fact is so common, and appears so natural and easy to understand, that we need not enter circumstantially into the causes. Want of organisation in the conquered land, and the very opposite effect which a serious loss instead of the looked-for fresh victory makes on the feelings, are the chief causes in every case. The moral forces, courage on the one side rising often to audacity, and extreme depression on the other, now begin generally their active play. The losses on the retreat are increased thereby, and the hitherto successful party now generally thanks providence if he can escape with only the surrender of all his gains, without losing some of his own territory.
We must now clear up an apparent contradiction.
It may be generally supposed that as long as progress in the attack continues, there must still be a preponderance; and, that as the defensive, which will commence at the end of the victorious career, is a stronger form of War than the offensive, therefore, there is so much the less danger of becoming unexpectedly the weaker party. But yet there is, and keeping history in view, we must admit that the greatest danger of a reverse is often just at the moment when the offensive ceases and passes into the defensive. We shall try to find the cause of this.
The superiority which we have attributed to the defensive form of War consists:
(1) In the use of ground.
(2) In the possession of a prepared theatre of War.
(3) In the support of the people.
(4) In the advantage of the state of expectancy.
It must be evident that these principles cannot always be forthcoming and active in a like degree; that, consequently, one defence is not always like another; and therefore, also, that the defence will not always have this same superiority over the offensive. This must be particularly the case in a defensive, which commences after the exhaustion of an offensive, and has its theatre of War usually situated at the apex of an offensive triangle thrust far forward into the country. Of the four principles above named, this defensive only enjoys the first—the use of the ground—undiminished, the second generally vanishes altogether, the third becomes negative, and the fourth is very much reduced. A few more words only, by way of explanation, respecting the last.
If the imagined equilibrium, under the influence of which whole campaigns have often passed without any results, because the side which should assume the initiative is wanting in the necessary resolution—and just therein lies, as we conceive, the advantage of the state of expectancy—if this equilibrium is disturbed by an offensive act, the enemy’s interests damaged, and his will stirred up to action, then the probability of his remaining in a state of indolent irresolution is much diminished. A defence, which is organised on conquered territory, has a much more irritating character than one upon our own soil; the offensive principle is engrafted on it in a certain measure, and its nature is thereby weakened. The quiet which Daun allowed Frederick II. in Silesia and Saxony, he would never have granted him in Bohemia.
Thus it is clear that the defensive, which is interwoven or mixed up with an offensive undertaking, is weakened in all its chief principles; and, therefore, will no longer have the preponderance which belongs to it originally.
As no defensive campaign is composed of purely defensive elements, so likewise no offensive campaign is made up entirely of offensive elements; because, besides the short intervals in every campaign, in which both sides are on the defensive, every attack which does not lead to a peace must necessarily end in a defensive.
In this manner it is the defensive itself which contributes to the weakening of the offensive. Thus is so far from being an idle subtlety, that on the contrary, we consider it a chief disadvantage of the attack that we are afterwards reduced through it to a very disadvantageous defensive.
And this explains how the difference which originally exists between the strength of the offensive and defensive forms in War is gradually reduced. We shall now show how it may completely disappear, and the advantage for a short time may change into the reverse.
If we may be allowed to make use of an idea from nature, we shall be able sooner to explain ourselves—the time which every force in the material world requires to show its effect. A power, which if applied slowly by degrees would be sufficient to check a body in motion, will be overcome by it if time fails. This law of the material world is a striking illustration of many of the phenomena in our inner life. If we are once roused to a certain train of thought, it is not every motive sufficient in itself which can change or stop that current of thought. Time, tranquillity and durable impressions on our senses are required. So it is also in War. When once the mind has taken a decided direction towards an object, or turned back towards a harbour of refuge, it may easily happen that the motives which in the one case naturally serve to restrain, and those which in the other as naturally excite to enterprise, are not felt at once in their full force; and as the progress of action in the meantime continues, one is carried along by the stream of movement beyond the line of equilibrium, beyond the culminating point, without being aware of it. Indeed, it may even happen that, in spite of the exhaustion of force, the assailant, supported by the moral forces which specially lie in the offensive, like a horse drawing a load uphill, finds it less difficult to advance than to stop. By this, we believe, we have now shown, without contradiction in itself, how the assailant may pass that point where, if he had stopped at the right moment, he might still, through the defensive, have had a result, that is equilibrium. Rightly, to determine this point is, therefore, important in framing a plan of a campaign, as well for the offensive, that he may not undertake what is beyond his powers (to a certain extent contract debts), as for the defensive, that he may perceive and profit by this error if committed by the assailant.
If now we look back at all the points which the Commander should bear in mind in making his determination, and remember that he can only estimate the tendency and value of the most important of them through the consideration of many other near and distant relations, that he must to a certain extent guess at them—guess whether the enemy’s Army, after the first blow, will show a stronger core and increasing solidity, or, like a Bologna phial, will turn into dust as soon as the surface is injured; guess the extent of weakness and prostration which the drying up of certain sources, the interruption of certain communications will produce on the military state of the enemy; guess whether the enemy, from the burning pain of the blow which has been dealt him, will collapse powerless, or whether, like a wounded bull, he will rise to a state of fury; lastly, guess whether other powers will be dismayed or roused, what political alliances are likely to be dissolved, and what are likely to be formed. When we say that he must hit all this, and much more, with the tact of his judgment, as the rifleman hits a mark, it must be admitted that such an act of the human mind is no trifle. A thousand wrong roads, running here and there, present themselves to the judgment; and whatever the number, the confusion, and complexity of objects leaves undone, is completed by the sense of danger and responsibility.
Thus it happens that the majority of Generals prefer to fall short of the mark rather than to approach too close; and thus it happens that a fine courage and great spirit of enterprise often go beyond the point, and therefore also fail to hit the mark. Only he that does great things with small means has made a successful hit.
PLAN OF WAR
[* ]See Chapters IV. and V.