On War
Clausewitz (1827)
The best Strategy is always to be very strong, first generally then at the decisive point. Therefore, apart from the energy which creates the Army, a work which is not always done by the General, there is no more imperative and no simpler law for Strategy than to keep the forces concentrated.--No portion is to be separated from the main body unless called away by some urgent necessity. On this maxim we stand firm, and look upon it as a guide to be depended upon. What are the reasonable grounds on which a detachment of forces may be made we shall learn by degrees. Then we shall also see that this principle cannot have the same general effects in every War, but that these are different according to the means and end.
It seems incredible, and yet it has happened a hundred times, that troops have been divided and separated merely through a mysterious feeling of conventional manner, without any clear perception of the reason.
If the concentration of the whole force is acknowledged as the norm, and every division and separation as an exception which must be justified, then not only will that folly be completely avoided, but also many an erroneous ground for separating troops will be barred admission.