On War

by Carl von Clausewitz

3. The attack from several quarters (all three, as in tactics).

4. The assistance of the theatre of war by fortresses, and everything belonging to them.

5. The support of the people.

6. The utilisation of great moral forces.

Now, what are the relations of offensive and defensive with respect to these things?

The party on the defensive has the advantage of ground; the offensive side that of the attack by surprise in strategy, as in tactics But respecting the surprise, we must observe that it is infinitely more efficacious and important in strategy than in tactics. In the latter, a surprise seldom rises to the level of a great victory, while in strategy it often finishes the war at one stroke. But at the same time we must observe that the advantageous use of this means supposes some great and uncommon, as well as decisive error committed by the adversary, therefore it does not alter the balance much in favour of the offensive.

The surprise of the enemy, by placing superior forces in position at certain points, has again a great resemblance to the analogous case in tactics. Were the defensive compelled to distribute his forces upon several points of approach to his theatre of war, then the offensive would have plainly the advantage of being able to fall upon one point with all his weight. But here also, the new art of acting on the defensive by a different mode of proceeding has imperceptibly brought about new principles. If the defensive side does not apprehend that the enemy, by making use of an undefended road, will throw himself upon some important magazine or depôt, or on some unprepared fortification, or on the capital itself.—and if he is not reduced to the alternative of opposing the enemy on the road he has chosen, or of having his retreat cut off, then there are no peremptory grounds for dividing his forces; for if the offensive chooses a different road from that on which the defensive is to be found, then some days later the latter can march against his opponent with his whole force upon the road he has chosen; besides, he may at the same time, in most cases, rest satisfied that the offensive will do him the honour to seek him out.—If the offensive is obliged to advance with his forces divided, which is often unavoidable on account of subsistence, then plainly the defensive has the advantage on his side of being able to fall in force upon a fraction of the enemy.

Attacks in flank and rear, which in strategy mean on the sides and reverse of the theatre of war, are of a very different nature to attacks so called in tactics.

1st. There is no bringing the enemy under two fires, because we cannot fire from one end of a theatre of war to the other.

2nd. The apprehension of losing the line of retreat is very much less, for the spaces in strategy are so great that they cannot be barred as in tactics.