Front Page Titles (by Subject) CHAPTER XVI: DEFENCE OF MOUNTAINS ( Continued ) - On War, vol. 2
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CHAPTER XVI: DEFENCE OF MOUNTAINS ( Continued ) - Carl von Clausewitz, On War, vol. 2 
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. 2.
Part of: On War
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DEFENCE OF MOUNTAINS (Continued)
We now proceed to the strategic use of the tactical results developed in the preceding chapter.
We make a distinction between the following points:—
1. A mountainous district as a battle-field.
2. The influence which the possession of it exercises on other parts of the country.
3. Its effect as a strategic barrier.
4. The attention which it demands in respect to the supply of the troops.
The first and most important of these heads, we must again subdivide as follows:—
A MOUNTAIN SYSTEM AS A BATTLE-FIELD.
We have shown in the preceding chapter how unfavourable mountain ground is to the defensive in a decisive battle, and, on the other hand, how much it favours the assailant. This runs exactly counter to the generally received opinion; but then how many other things there are which general opinion confuses; how little does it draw distinctions between things which are of the most opposite nature! From the powerful resistance which small bodies of troops may offer in a mountainous country, common opinion becomes impressed with an idea that all mountain defence is extremely strong, and is astonished when any one denies that this great strength is communicated to the greatest act of all defence, the defensive battle. On the other hand, it is instantly ready, whenever a battle is lost by the defensive in mountain warfare, to point out the inconceivable error of a system of cordon war, without any regard to the fact that in the nature of things such a system is unavoidable in mountain warfare. We do not hesitate to put ourselves in direct opposition to such an opinion, and at the same time we must mention, that to our great satisfaction, we have found our views supported in the works of an author whose opinion ought to have great weight in this matter; we allude to the history of the campaigns of 1796 and 1797, by the Archduke Charles, himself a good historical writer, a good critic, and above all, a good General.
We can only characterise it as a lamentable position when the weaker defender, who has laboriously, by the greatest effort, assembled all his forces, in order to make the assailant feel the effect of his love of Fatherland, of his enthusiasm and his ability, in a decisive battle—when he on whom every eye is fixed in anxious expectation, having betaken himself to the obscurity of thickly veiled mountains, and hampered in every movement by the obstinate ground, stands exposed to the thousand possible forms of attack which his powerful adversary can use against him. Only towards one single side is there still left an open field for his intelligence, and that is in making all possible use of every obstacle of ground; but this leads close to the borders of the disastrous war of cordons, which, under all circumstances, is to be avoided. Very far therefore from seeing a refuge for the defensive, in a mountainous country, when a decisive battle is sought, we should rather advise a General in such a case to avoid such a field by every possible means.
It is true, however, that this is sometimes impossible; but the battle will then necessarily have a very different character from one in a level country: the disposition of the troops will be much more extended—in most cases twice or three times the length; the resistance more passive, the counter blow much less effective. These are influences of mountain ground which are inevitable; still, in such a battle the defensive is not to be converted into a mere defence of mountains; the predominating character must be a concentrated order of battle in the mountains, in which everything unites into one battle, and passes as much as possible under the eye of one Commander, and in which there are sufficient reserves to make the decision something more than a mere warding off, a mere holding up of the shield. This condition is indispensable, but difficult to realise; and the drifting into the pure defence of mountains comes so naturally, that we cannot be surprised at its often happening; the danger in this is so great that theory cannot too urgently raise a warning voice.
Thus much as to a decisive battle with the main body of the Army.—
For combats of minor significance and importance, a mountainous country, on the other hand, may be very favourable, because the main point in them is not absolute defence, and because no decisive results are coupled with them. We may make this plainer by enumerating the objects of this reaction.
a. Merely to gain time. This motive occurs a hundred times: always in the case of a defensive line formed with the view of observation; besides that, in all cases in which a reinforcement is expected.
b. The repulse of a mere demonstration or minor enterprise of the enemy. If a province is guarded by mountains which are defended by troops, then his defence, however weak, will always suffice to prevent partisan attacks and expeditions intended to plunder the country. Without the mountains, such a weak chain of posts would be useless.
c. To make demonstrations on our own part. It will be some time yet before general opinion with respect to mountains will be brought to the right point; until then an enemy may at any time be met with who is afraid of them, and shrinks back from them in his undertakings. In such a case, therefore, the principal body may also be used for the defence of a mountain system. In Wars carried on with little energy or movement, this state of things will often happen; but it must always be a condition then that we neither design to accept a general action in this mountain position, nor can be compelled to do so.
d. In general, a mountainous country is suited for all positions in which we do not intend to accept any great battle, for each of the separate parts of the Army is stronger there, and it is only the whole that is weaker; besides, in such a position, it is not so easy to be suddenly attacked and forced into a decisive battle.
e. Lastly, a mountainous country is the true region for the efforts of a people in arms. But while national risings should always be supported by small bodies of regular troops, on the other hand, the proximity of a great Army seems to have an unfavourable effect upon movements of this kind; this motive, therefore, as a rule, will never give occasion for transferring the whole Army to the mountains.
Thus much for mountains in connection with the positions which may be taken up there for battle.
THE INFLUENCE OF MOUNTAINS ON OTHER PARTS OF THE COUNTRY.
Because, as we have seen, it is so easy in mountainous ground to secure a considerable tract of territory by small posts, so weak in numbers that in a district easily traversed they could not maintain themselves, and would be continually exposed to danger; because every step forward in mountains which have been occupied by the enemy must be made much more slowly than in a level country, and therefore cannot be made at the same rate with him—therefore the question, Who is in possession?—is also much more important in reference to mountains than to any other tract of country of equal extent. In an open country, the possession may change from day to day. The mere advance of strong detachments compels the enemy to give up the country we want to occupy. But it is not so in mountains; there a very stout resistance is possible by much inferior forces, and for that reason, if we require a portion of country which includes mountains, enterprises of a special nature, formed for the purpose, and often necessitating a considerable expenditure of time as well as of men, are always required in order to obtain possession. If, therefore, the mountains of a country are not the theatre of the principal operations of a War, we cannot, as we should were it the case of a district of level country, look upon the possession of the mountains as dependent on and a necessary consequence of our success at other parts.
A mountainous district has therefore much more independence, and the possession of it is much firmer and less liable to change. If we add to this that a ridge of mountains from its crests affords a good view over the adjacent open country, whilst it hides the district behind it, we may therefore conceive that when we are close to mountains, without being in actual possession of them, they are to be regarded as a constant source of disadvantage—a sort of laboratory of hostile forces; and this will be the case in a still greater degree if the mountains are not only occupied by the enemy, but also form part of his territory. The smallest bodies of adventurous partisans always find shelter there if pursued, and can then sally forth again with impunity at other points; the largest bodies, under their cover, can approach unperceived, and our forces must, therefore, always keep at a sufficient distance if they would avoid getting within reach of their dominating influence—if they would not be exposed to disadvantageous combats and sudden attacks which they cannot return.
In this manner every mountain system exercises a very great influence over the lower and more level country adjacent to it, up to a certain distance. Whether this influence shall take effect momentarily, for instance in a battle (as at Maltsch on the Rhine, 1796) or only after some time upon the lines of communication, depends on the local relations;—whether or not it shall be overcome through some decisive event happening in the valley or level country, depends on the relations of the armed forces to each other respectively.
Buonaparte, in 1805 and 1809, advanced upon Vienna without troubling himself much about the Tyrol; but Moreau had to leave Swabia in 1796, chiefly because he was not master of the more elevated parts of the country, and too many troops were required to watch them. In campaigns, in which there is an evenly balanced series of alternate successes on each side, we shall not expose ourselves to the constant disadvantage of the mountains remaining in possession of the enemy: we need, therefore, only endeavour to seize and retain possession of that portion of them which is required on account of the direction of the principal lines of our attack; this generally leads to the mountains being the arena of the separate minor combats which take place between forces on each side. But we must be careful of overrating the importance of this circumstance, and being led to consider a mountain-chain as the key to the whole in all cases, and its possession as the main point. When a victory is the object sought; then it is the principal object; and if the victory is gained, other things can be regulated according to the paramount requirement of the situation.
MOUNTAINS CONSIDERED IN THEIR ASPECT OF A STRATEGIC BARRIER.
We must divide this subject under two heads.
The first is again that of a decisive battle. We can, for instance, consider the mountain chain as a river, that is, as a barrier with certain points of passage, which may afford us an opportunity of gaining a victory, because the enemy will be compelled by it to divide his forces in advancing, and is tied down to certain roads, which will enable us with our forces concentrated behind the mountains to fall upon fractions of his force. As the assailant on his march through the mountains, irrespective of all other considerations, cannot march in a single column because he would thus expose himself to the danger of getting engaged in a decisive battle with only one line of retreat, therefore, the defensive method recommends itself certainly on substantial grounds. But as the conception of mountains and their outlets is very undefined, the question of adopting this plan depends entirely on the nature of the country itself, and it can only be pointed out as possible whilst it must also be considered as attended with two disadvantages, the first is, that if the enemy receives a severe blow, he soon finds shelter in the mountains; the second is, that he is in possession of the higher ground, which, although not decisive, must still always be regarded as a disadvantage for the pursuer.
We know of no battle given under such circumstances unless the battle with Alvinzi in 1796 can be so classed. But that the case may occur is plain from Buonaparte’s passage of the Alps in the year 1800, when Melas might and should have fallen on him with his whole force before he had united his columns.
The second influence which mountains may have as a barrier is that which they have upon the lines of communication if they cross those lines. Without taking into account what may be done by erecting forts at the points of passage and by arming the people, the bad roads in mountains at certain seasons of the year may of themselves alone prove at once destructive to an Army; they have frequently compelled a retreat after having first sucked all the marrow and blood out of the Army. If, in addition, troops of active partisans hover round, or there is a national rising to add to the difficulties, then the enemy is obliged to make large detachments, and at last driven to form strong posts in the mountains and thus gets engaged in one of the most disadvantageous situations that can be in an offensive War.
MOUNTAINS IN THEIR RELATION TO THE PROVISIONING AN ARMY.
This is a very simple subject, easy to understand. The opportunity to make the best use of them in this respect is when the assailant is either obliged to remain in the mountains, or at least to leave them close in his rear.
These considerations on the defence of mountains, which, in the main, embrace all mountain warfare, and, by their reflection, throw also the necessary light on offensive War, must not be deemed incorrect or impracticable because we can neither make plains out of mountains, nor hills out of plains, and the choice of a theatre of War is determined by so many other things that it appears as if there was little margin left for considerations of this kind. In affairs of magnitude it will be found that this margin is not so small. If it is a question of the disposition and effective employment of the principal force, and that, even in the moment of a decisive battle, by a few marches more to the front or rear an Army can be brought out of mountain ground into the level country, then a resolute concentration of the chief masses in the plain will neutralise the adjoining mountains.
We shall now once more collect the light which has been thrown on the subject, and bring it to a focus in one distinct picture.
We maintain and believe we have shown, that mountains, both tactically and strategically, are in general unfavourable to the defensive, meaning thereby, that kind of defensive which is decisive, on the result of which the question of the possession or loss of the country depends. They limit the view and prevent movements in every direction; they force a state of passivity, and make it necessary to stop every avenue or passage, which always leads more or less to a war of cordons. We should therefore, if possible, avoid mountains with the principal mass of our force, and leave them on one side, or keep them before or behind us.
At the same time, we think that, for minor operations and objects, there is an element of increased strength to be found in mountain ground; and after what has been said, we shall not be accused of inconsistency in maintaining that such a country is the real place of refuge for the weak, that is, for those who dare not any longer seek an absolute decision. On the other hand again, the advantages derived from a mountainous country by troops acting an inferior rôle cannot be participated in by large masses of troops.
Still all these considerations will hardly counteract the impressions made on the senses. The imagination not only of the inexperienced but also of all those accustomed to bad methods of War will still feel in the concrete case such an overpowering dread of the difficulties which the inflexible and retarding nature of mountainous ground oppose to all the movements of an assailant, that they will hardly be able to look upon our opinion as anything but a most singular paradox. Then again, with those who take a general view, the history of the last century (with its peculiar form of War) will take the place of the impression of the senses, and therefore there will be but few who will not still adhere to the belief that Austria, for example, should be better able to defend her states on the Italian side than on the side of the Rhine. On the other hand, the French who carried on War for twenty years under a leader both energetic and indifferent to minor considerations, and have constantly before their eyes the successful results thus obtained, will, for some time to come, distinguish themselves in this as well as in other cases by the tact of a practised judgment.
Does it follow from this that a State would be better protected by an open country than by mountains, that Spain would be stronger without the Pyrenees; Lombardy more difficult of access without the Alps, and a level country such as North Germany more difficult to conquer than a mountainous country? To these false deductions we shall devote our concluding remarks.
We do not assert that Spain would be stronger without the Pyrenees than with them, but we say that a Spanish Army, feeling itself strong enough to engage in a decisive battle, would do better by concentrating itself in a position behind the Ebro, than by distributing itself amongst the fifteen passes of the Pyrenees. But the influence of the Pyrenees on War is very far from being set aside on that account. We say the same respecting an Italian Army. If it divided itself in the High Alps it would be vanquished by each resolute Commander it encountered, without even the alternative of victory or defeat; whilst in the plains of Turin it would have the same chance as every other Army. But still no one can on that account suppose that it is desirable for an aggressor to have to march over masses of mountains such as the Alps, and to leave them behind. Besides, a determination to accept a great battle in the plains, by no means excludes a preliminary defence of the mountains by subordinate forces, an arrangement very advisable in respect to such masses as the Alps and Pyrenees. Lastly, it is far from our intention to argue that the conquest of a mountainous country is easier than that of a level* one, unless a single victory sufficed to prostrate the enemy completely. After this victory ensues a state of defence for the conqueror, during which the mountainous ground must be as disadvantageous to the assailant as it was to the defensive, and even more so. If the War continues, if foreign assistance arrives, if the people take up arms, this reaction will gain strength from a mountainous country.
It is here as in dioptrics, the image represented becomes more luminous when moved in a certain direction, not, however, as far as one pleases, but only until the focus is reached, beyond that the effect is reversed.
If the defensive is weaker in the mountains, that would seem to be a reason for the assailant to prefer a line of operations in the mountains. But this will seldom occur, because the difficulties of supporting an Army, and those arising from the roads, the uncertainty as to whether the enemy will accept battle in the mountains, and even whether he will take up a position there with his principal force, tend to neutralise that possible advantage.
[* ]As it is conceived that the words “ebenen” and “gebirgigen” in this passage in the original have by some means become transposed, their equivalents—level and mountainous—are here placed in the order in which it is presumed the author intended the words to stand.—Tr.