We have considered the voluntary retreat into the heart of the country as a particular indirect form of defence through which it is expected the enemy will be destroyed, not so much by the sword as by exhaustion from his own efforts. In this case, therefore, a great battle is either not supposed, or it is assumed to take place when the enemy’s forces are considerably reduced.
Every assailant in advancing diminishes his military strength by the advance; we shall consider this more in detail in the seventh book; here we must assume that result which we may the more readily do as it is clearly shown by military history in every campaign in which there has been a considerable advance.
This loss in the advance is increased if the enemy has not been beaten, but withdraws of his own accord with his forces intact, and offering a steady continuous resistance, sells every step of ground at a bloody price, so that the advance is a continuous combat for ground and not a mere pursuit.
On the other hand, the losses which a party on the defensive suffers on a retreat, are much greater if his retreat has been preceded by a defeat in battle than if his retreat is voluntary. For if he is able to offer the pursuer the daily resistance which we expect on a voluntary retreat, his losses would be at least the same in that way, over and above which those sustained in the battle have still to be added. But how contrary to the nature of the thing such a supposition as this would be! The best army in the world if obliged to retire far into the country after the loss of a battle,