On War

by Carl von Clausewitz

4. Because many disadvantages of the weak points of the aggression disappear when the defender’s army is divided into separate parts.

The weakest features in a long advance on the part of the aggressor are for instance;—the length of the lines of communication, and the exposure of the strategic flanks. By the divergent form of retreat, the aggressor is compelled to cause a portion of his force to show a front to the flank, and this portion properly destined only to neutralise our force immediately in his front, now effects to a certain extent something else in addition, by covering a portion of the lines of communication.

For the mere strategic effect of the retreat, the divergent form is therefore not favourable; but if it is to prepare an action hereafter against the enemy’s line of retreat, then we must refer to what has been said about that in the last chapter.

There is only one object which can give occasion to a divergent retreat, that is when we can by that means protect provinces which otherwise the enemy would occupy.

What sections of territory the advancing foe will occupy right and left of his course, can with tolerable accuracy be discerned by the point of assembly of, and directions given to, his forces, by the situation of his own provinces, fortresses, etc., in respect to our own. To place troops in those districts of territory which he will in all probability leave unoccupied, would be dangerous waste of our forces. But now whether by any disposition of our forces we shall be able to hinder him from occupying those districts which in all probability he will desire to occupy, is more difficult to decide, and it is therefore a point, the solution of which depends much on tact of judgment.

When the Russians retreated in 1812, they left 30,000 men under Tormassow in Volhynia, to oppose the Austrian force which was expected to invade that province. The size of the province, the numerous obstacles of ground which the country presents, the near proportion between the forces likely to come into conflict justified the Russians in their expectations, that they would be able to keep the upper hand in that quarter, or at least to maintain themselves near to their frontier. By this, very important advantages might have resulted in the sequel, which we shall not stop here to discuss; besides this, it was almost impossible for these troops to have joined the main army in time if they had wished. For these reasons, the determination to leave these troops in Volhynia to carry on there a distinct war of their own, was right. Now on the other hand, if according to the proposed plan of campaign submitted by General Phul, only the army of Barclay (80,000 men), was to retire to Drissa, and Bragathion’s army (40,000 men) was to remain on the right flank of the French, with a view to subsequently falling on their rear, it is evident at once that this corps could not possibly maintain itself in South Lithuania so near to the rear of the main body of the French army, and would soon have been destroyed by their overwhelming masses.

That the defender’s interest in itself is to give up as few provinces as possible to the assailant is intelligible enough, but this is always a secondary consideration; that the attack is also made more difficult the smaller or rather narrower the theatre of war is to which we can confine the enemy, is likewise clear in itself; but all this is subordinate to the condition that in so doing we have the probability of a result in our favour, and that the main body of the force on the defensive will not be too much weakened; for upon that force we must chiefly depend for the final solution, because the difficulties and distress suffered by the main body of the enemy, first call forth his determination to retreat, and increase in the greatest degree the loss of physical and moral power therewith connected.

The retreat into the interior of the country should therefore as a rule be made directly before the enemy, and as slowly as possible, with an army which has not suffered defeat and is undivided; and by its incessant resistance it should force the enemy to a constant state of readiness for battle, and to a ruinous expenditure of forces in tactical and strategical measures of precaution.

When both sides have in this manner reached the end of the aggressor’s first start, the defender should then dispose his army in a position, if such can be found, forming an oblique angle with the route of his opponent, and operate against the enemy’s rear with all the means at his command.

The campaign of 1812 in Russia shows all these measures on a great scale, and their effects, as it were, in a magnifying glass. Although it was not a voluntary retreat, we may easily consider it from that point of view. If the Russians with the experience they now have of the results to be thus produced, had to undertake the defence of their country over again, exactly under the same circumstances, they would do voluntarily and systematically what in great part was done without a definite plan in 1812; but it would be a great mistake to suppose that there neither is nor can be any instance elsewhere of the same mode of action where the dimensions of the Russian empire are wanting.