Defence of a Theatre of War

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The defensive, according to our conception, is nothing but the stronger form of combat. The preservation of our own forces and the destruction of those of the enemy -- in a word, the victory -- is the aim of this contest, but at the same time not its ultimate object.

That object is the preservation of our own political state and the subjugation of that of the enemy; or again, in one word, the desired peace, because it is only by it that this conflict adjusts itself, and ends in a common result.

But what is the enemy’s state in connection with war? Above all things its military force is important, then its territory; but certainly there are also still many other things which, through particular circumstances, may obtain a predominant importance; to these belong, before all, foreign and domestic political relations, which sometimes decide more than all the rest. But although the military force and the territory of the enemy alone are still not the state itself, nor are they the only connections which the state may have with the war, still these two things are always preponderating, mostly immeasurably surpassing all other connections in importance. Military force is to protect the territory of the state, or to conquer that of an enemy; the territory on the other hand, constantly nourishes and renovates the military force. The two, therefore, depend on each other, mutually support each other, are equal in importance one to the other. But still there is a difference in their mutual relations. If the military force is destroyed, that is completely defeated, rendered incapable of further resistance, then the loss of the territory follows of itself; but on the other hand, the destruction of the military force by no means follows from the conquest of the country, because that force may of its own accord evacuate the territory in order afterwards to reconquer it the more easily. Indeed, not only does the complete destruction of its army decide the fate of a country, but even every considerable weakening of its military force leads regularly to a loss of territory; on the other hand, every considerable loss of territory does not cause a proportionate diminution of military power; in the long run it will do so, but not always within the space of time in which a war is brought to a close.

From this it follows that the preservation of our own military power, and the diminution or destruction of that of the enemy, take precedence in importance over the occupation of territory, and, therefore, is the first object which a general should strive for. The possession of territory only presses for consideration as an object if that means (diminution or destruction of the enemy’s military force) has not effected it.

If the whole of the enemy’s military power was united in one army, and if the whole war consisted of one battle, then the possession of the country would depend on the issue of that battle; destruction of the enemy’s military forces, conquest of his country and security of our own, would follow from that result, and, in a certain measure, be identical with it. Now the question is, what can induce the defensive to deviate from this simplest form of the act of warfare, and distribute his power in space? The answer is, the insufficiency of the victory which he might gain with all his forces united. Every victory has its sphere of influence. If this extends over the whole of the enemy’s state, consequently over the whole of his military force and his territory, that is, if all the parts are carried along in the same movement, which we have impressed upon the core of his power, then such a victory is all that we require, and a division of our forces would not be justified by sufficient grounds. But if there are portions of the enemy’s military force, and of country belonging to either party, over which our victory would have no effect, then we must give particular attention to those parts; and as we cannot unite territory like a military force in one point, therefore we must divide our forces for the purpose of attacking or defending those portions.
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The effect of a victory will naturally depend on its greatness, and that on the mass of the conquered troops. Therefore the blow which, if successful, will produce the greatest effect, must be made against that part of the country where the greatest number of the enemy’s forces are collected together; and the greater the mass of our own forces which we use for this blow, so much the surer shall we be of this success. This natural sequence of ideas leads us to an illustration by which we shall see this truth more clearly; it is the nature and effect of the centre of gravity in mechanics.