The lesson of this trench warfare, therefore, is that if a combatant retires before it is too late he has every chance to survive to fight another day; and he has all the more chance of a new offensive, or at least of maintaining a strong defensive, if he retires in the direction of his resources, or what is called his line of operation, whence he receives his munitions, food and material of war. He retires from the battle, therefore, at the psychological moment when he sees he is likely to be overwhelmed, and reconstitutes himself in the rear. The opening phases of 1914 gave us two parallel retreats: from the Belgian frontier to the Seine by the Allies, and from the Marne to the Aisne by the Germans. The campaign in Poland also showed a similar disposition, and the Russians reformed their line and beat the Germans after they retreated before them. Therefore a mere retreat may be, literally, little more than a strategic movement in the rear. It does not mean, certainly, that all is lost or that the position of the retreating force is one of utter hopelessness. After the opening phases of the war, the subterranean character of the fighting was maintained, until such big offensives as Verdun re-evoked the old-time battle, when the Kaiser watched the operations from an eminence, and on a front of twenty miles scenes of the old onslaught were re-enacted. But in this case the initiative was left to the Germans. To them also the greater part of the losses, for whilst they manoeuvred in the open and hurled masses of their grey-green warriors upon the French trenches, the defenders enfiladed the masses and mowed them down with the gigantic scythes that their science had forged since the war began. A curious feature of the fighting in the Great War was the element of fatigue. We have met with it everywhere. It follows closely the course of the war; it is seen in every phase. At Charleroi and Mons and those terrific fights that marked the beginning of the war, the retreating armies of England and France escaped because of the exhaustion of the Germans. If cavalry had harried their rearguards and mobile cannon had cannonaded their flanks the retreat might have been turned into a rout. For the French, largely composed of reservists, were within an ace of demoralisation. And again the Allies, as conquerors, showed extreme fatigue in the battle of the Marne, when the victory might have been more decisive had it been followed up by unwearied troops, or, again, by masses of cavalry.