On War

by Carl von Clausewitz

To such a risk we say the defender may very well expose himself, if he has, on the other hand, the possibility, or rather the probability, in his favour, that the assailant from excessive caution will halt before his posts without attacking them. Only in regard to this we must not lose sight of the fact, that we are now supposing an assailant who will not venture upon any great stroke, a moderate sized, but strong post will very well serve to stop such an adversary, for although he can undoubtedly make himself master of it, still the question arises as to the price it will cost, and whether that price is not too high for any use that he can make of the victory.

In this way we may see how the powerful relative resistance which the defender can obtain from an extended disposition, consisting of a number of posts in juxtaposition with each other, may constitute a satisfactory result in the calculation of his whole campaign. In order to direct at once to the right point the glance which the reader, with his mind’s eye, will here cast upon military history, we must observe that these extended positions appear most frequently in the latter half of a campaign, because by that time the defender has become thoroughly acquainted with his adversary, with his projects, and his situation; and the little quantity of the spirit of enterprise with which the assailant started, is usually exhausted.

In this defensive, in an extended position by which the country, the supplies, the fortresses are to be covered, all great natural obstacles, such as streams, rivers, mountains, woods, morasses, must naturally play a great part, and acquire a predominant importance. Upon their use we refer to what has been already said on these subjects.

It is through this predominant importance of the topographical element that the knowledge and activity which are looked upon as the speciality of the general staff of an army are more particularly called into requisition. Now, as the staff of the army is usually that branch which writes and publishes most, it follows that these parts of campaigns are recorded more fully in history; and then again from that there follows a not unnatural tendency to systematise them, and to frame out of the historical solution of one case a general solution for all succeeding cases. But this endeavour is futile, and therefore erroneous. Besides, in this more passive kind of war, in this form of it which is tied to localities, each case is different to another, and must be differently treated. The ablest memoirs of a critical character respecting these subjects are therefore only suited to make one acquainted with facts, but never to serve as dictates.

Natural, and at the same time meritorious, as is this industry which, according to the general view, we have attributed to the staff in particular, still we must raise a warning voice against usurpations which often spring from it to the prejudice of the whole. The authority acquired by those who are at the head of, and best acquainted with, this branch of military service, gives them often a sort of general dominion over people’s minds, beginning with the general himself, and from this then springs a routine of ideas which causes an undue bias of the mind. At last the general sees nothing but mountains and passes, and that which should be a measure of free choice guided by circumstances becomes mannerism, becomes second nature.

Thus in the year 1793 and 1794, Colonel Grawert of the Prussian army, who was the animating spirit of the staff at that time, and well known as a regular man for mountains and passes, persuaded two generals of the most opposite personal characteristics, the Duke of Brunswick and General Mollendorf, into exactly the same method of carrying on war.

That a defensive line parallel to the course of a formidable natural obstacle may lead to a cordon war is quite plain. It must, in most cases, necessarily lead to that if really the whole extent of the theatre of war could be directly covered in that manner. But most theatres of war have such an extent, that the normal tactical disposition of the troops destined for its defence would be by no means commensurate with that object; at the same time as the assailant, by his own dispositions and other circumstances, is confined to certain principal directions and great roads, and any great deviations from these directions, even if he is only opposed to a very inactive defender, would be attended with great embarrassment and disadvantage, therefore generally all that the defender has to do is to cover the country for a certain number of miles or marches right and left of these principal lines of direction of his adversary. But again to effect this covering, we may be contented with defensive posts on the principal roads and means of approach, and merely watch the country between by small posts of observation. The consequence of this is certainly that the assailant may then pass a column between two of these posts, and thus make the attack, which he has in view, upon one post from several quarters at once. Now, these posts are in some measure arranged to meet this, partly by their having supports for their flanks, partly by the formation of flank defences (called crochets), partly by their being able to receive assistance from a reserve posted in rear, or by troops detached from adjoining posts. In this manner the number of posts is reduced still more, and the result is that an army engaged in a defence of this kind, usually divides itself into four or five principal posts.

For important points of approach, beyond a certain distance, and yet in some measure threatened, special central points are established which, in a certain measure, form small theatres of war within the principal one. In this manner the Austrians, during the Seven Years’ War, generally placed the main body of their army, in four or five posts in the mountains of Lower Silesia; whilst a small almost independent corps organised for itself a similar system of defence in Upper Silesia.

Now, the further such a defensive system diverges from direct covering, the more it must call to its assistance—mobility (active defence), and even offensive means. Certain corps are considered reserves; besides which, one post hastens to send to the help of another all the troops it can spare. This assistance may be rendered either by hastening up directly from the rear to reinforce and re-establish the passive defence, or by attacking the enemy in flank, or even by menacing his line of retreat. If the assailant threatens the flank of a post not with direct attack, but only by a position through which he can act upon the communications of this post, then either the corps which has been advanced for this purpose must be attacked in earnest, or the way of reprisal must be resorted to by acting in turn on the enemy’s communications.

We see, therefore, that however passive this defence is in the leading ideas on which it is based, still it must comprise many active means, and in its organisation may be forearmed in many ways against complicated events. Usually those defences pass for the best which make the most use of active or even offensive means; but this depends in great part on the nature of the country, the characteristics of the troops, and even on the talent of the general; partly we are also very prone in general to expect too much from movement, and other auxiliary measures of an active nature, and to place too little reliance on the local defence of a formidable natural obstacle. We think we have thus sufficiently explained what we understand by an extended line of defence, and we now turn to the third auxiliary means, the placing ourselves in front of the enemy by a rapid march to a flank.