This is one of the principal points in strategy: on its right valuation
in the concrete, depends our being able to judge correctly what we are
able to do.
The decrease of absolute power arises—
1. Through the object of the attack, the occupation of the enemy’s
country; this generally commences first after the first decision, but
the attack does not cease upon the first decision.
2. Through the necessity imposed on the attacking army to guard the
country in its rear, in order to preserve its line of communication and
means of subsistence.
3. Through losses in action and through sickness.
4. Distance of the various depôts of supplies and reinforcements.
5. Sieges and blockades of fortresses.
6. Relaxation of efforts.
7. Secession of allies.
But frequently, in opposition to these weakening causes, there may be
many others which contribute to strengthen the attack. It is clear, at
all events, that a net result can only be obtained by comparing these
different quantities; thus, for example, the weakening of the attack
may be partly or completely compensated, or even surpassed by the
weakening of the defensive. This last is a case which rarely happens;
we cannot always bring into the comparison any more forces than those
in the immediate front or at decisive points, not the whole of the
forces in the field.—Different examples: The French in Austria and
Prussia, in Russia; the allies in France, the French in Spain.