In the first place, our forces must be sufficient,—
1. To gain a decisive victory over those of the enemy.
2. To make the expenditure of force which may be necessary to follow up the victory to a point at which it will no longer be possible for the enemy to regain his balance.
Next, we must feel sure that in our political situation, such a result will not excite against us new enemies, who may compel us on the spot to set free our first enemy.
France, in the year 1806, was able completely to conquer Prussia, although in doing so it brought down upon itself the whole military power of Russia, because it was in a condition to cope with the Russians in Prussia.
France might have done the same in Spain in 1808 as far as regards England, but not as regards Austria. It was compelled to weaken itself materially in Spain in 1809, and must have quite given up the contest in that country if it had not had otherwise great superiority both physically and morally, over Austria.
These three cases should therefore be carefully studied, that we may not lose in the last the cause which we have gained in the former ones, and be condemned in costs.
In estimating the strength of forces, and that which may be effected by them, the idea very often suggests itself to look upon time by a dynamic analogy as a factor of forces, and to assume accordingly that half efforts, or half the number of forces would accomplish in two years what could only be effected in one year by the whole force united. This view which lies at the bottom of military schemes, sometimes clearly, sometimes less plainly, is completely wrong.
An operation in war, like everything else upon earth, requires its time; as a matter of course we cannot walk from Wilna to Moscow in eight days; but there is no trace to be found in war of any reciprocal action between time and force, such as takes place in dynamics.
Time is necessary to both belligerents, and the only question is: which of the two, judging by his position, has most reason to expect special advantages from time? Now (exclusive of peculiarities in the situation on one side or the other) the vanquished has plainly the most reason, at the same time certainly not by dynamic, but by psychological laws. Envy, jealousy, anxiety for self, as well as now and again magnanimity, are the natural intercessors for the unfortunate; they raise up for him on the one hand friends, and on the other hand weaken and dissolve the coalition amongst his enemies. Therefore, by delay something advantageous is more likely to happen for the conquered than for the conqueror. Further, we must recollect that to make right use of a first victory, as we have already shown, a great expenditure of force is necessary; this is not a mere outlay once for all, but has to be kept up like housekeeping, on a great scale; the forces which have been sufficient to give us possession of a province, are not always sufficient to meet this additional outlay; by degrees the strain upon our resources becomes greater, until at last it becomes insupportable; time, therefore, of itself may bring about a change.