According to Clausewitz, war must be subject to the one supreme law of decision by force of arms. In this sense did Frederick the Great, Napoleon, and Moltke conduct their operations. With them it was a question of the annihilation of the enemy's forces, not of the winning and keeping of provinces. If the entrenched battles of the present War had for their purpose the holding of ground that had been won, none the less the implied contradiction with the theories of the greatest generals of modern times is only apparent. In the World War it was a question of battle-fronts which we held and in contending for which our opponents sacrificed the blood of their troops, and not of a cordon of positions after the fashion of those of the eighteenth century. The entrenched lines of that time served principally to keep the enemy at a distance, and as far as possible to obviate a pitched battle. Considering the inadequacy of the means of attack at that time and of the old hired armies, as well as the inferior mobility and deficient driving force of a linear _ordre de bataille_ they frequently fulfilled their purpose. When, however, war was dominated by the will of a powerful leader, it took on immediately quite a different aspect. Nevertheless it must not be overlooked that even Napoleon frequently advocates entrenched positions, and that he himself at times, when his troops had been brought to a standstill, had recourse to them, for instance in 1807 at the Passarge, and in the autumn of 1813, when, though his defence remained mobile, he constructed extensive temporary fortifications on the Elbe. Frederick the Great, too, finally adapted himself to a Bunzelwitz. Already at the conclusion of the campaign of 1758, he admitted[8] that to attack the enemy without having first secured for oneself a superiority as regards firearms would be much as if a mob armed with cudgels were to engage an armed military force; that it was necessary to adopt the Austrian system of a powerful artillery, however inconvenient this might be; and that lessons might be learnt from the enemy in regard to the skilful exploitation of the ground. "The best infantry in the world," he said, "may in certain cases be thrown into disorder, when it has to contend against the enemy, his guns, and disadvantages of ground. Our own infantry, enfeebled and demoralised alike by victories and defeats, demand to be sparingly employed for difficult undertakings. One must be guided by a consideration of their intrinsic worth." After the Seven Years' War, the King gave even more emphatic expression to these views in the military section of his _Politisches Testament vom Jahre 1768_. In this he says: "We must reckon upon the possibility of a mere contest for entrenched positions (_Postenkrieg_) with the Austrians"; and he says further: