After the Battle of the Marne, the War in the West assumed on the German side first of all the character of a defence accompanied by offensive tactics, and subsequently, after the attack at the Yser had proved unsuccessful and when further troops had to be conveyed to the East, was completely transformed at the end of November, 1914, into an entrenched war. It ought, however, to be realised that though in the World War entrenched fighting has gained such prevalence and importance, this is not necessarily a result of the highly developed technical science of our age, but first and foremost the result of the inability of our enemies to break through the German fronts in the East and the West. If the armies of the two contending parties had been equally efficient, it would have been impossible for us to maintain our positions for any length of time, in view of the overwhelming numerical superiority of the forces which were directed against ourselves and Austria-Hungary from all sides. It lay with our opponents with their vast numbers, when they had forced us to retreat, to give to the War once again the character of a war of movement. They did not succeed in doing so. On the other hand, the forces of the Central Powers were insufficient to enable them to push the offensive to any considerable extent beyond the permanent positions taken up on the Western front at the end of 1914 and on the Eastern front in the autumn of 1915, and on their side to pass once more to the war of movement. This was reserved in the further course of events for the Serbian and (a year later) the Roumanian theatres of war. In view of our central position, we were obliged, since we had not succeeded in breaking through at the Marne, to content ourselves with an "offensive with a limited goal," to use the words of Clausewitz. He says further: "A defence which is organised on conquered territory has a much more irritating character than one upon our own soil: The offensive principle is engrafted on it in a certain measure."[7] The course of the World War has quite confirmed this. But at the same time this view involves the admission that the maintenance of such a defence ought in itself to be considered as an important success. Apart from this offensive defensive, the only possibility for the Central Powers could be to anticipate the enemy's actions in particular cases, as was done by our army at Verdun and by the Austro-Hungarian army in the Venetian Alps; the initiative as a whole we were obliged to leave to the enemy. Consequently, we were driven to the tenacious, to a large extent passive, retention of our entrenched lines, and to their consolidation with the aid of every means furnished by the art of field-fortification.