_That is exactly what happened in the first three weeks of active operations in the West. The operative corner A in the annexed diagram was the Franco-British force upon the Sambre. The retirement of that operative corner and its holding of the enemy was what is called in this country "The Retreat from Mons." BB are the "masses of manoeuvre" behind A. The swinging up of these masses involving the retirement of the whole was the Battle of the Marne._ [Illustration: Sketch 31.] Now, it is evident that in all this everything depends upon the tenacity and military value of the operative corner, which is exposed and sacrificed that the whole scheme of the Open Square may work. If that operative corner is destroyed as a force--is overwhelmed or dispersed or surrounded--while it is fighting its great odds, the whole square goes to pieces. Its centre is penetrated by the enemy, and the army is in a far worse plight than if recourse had never been had to the open strategic square at all. For if the operative corner, A, is out of existence before the various bodies forming the "manoeuvring mass" behind it have had time to "swing," then the enemy will be right in their midst, and destroying, in overwhelming force, these remaining _separated_ bodies in detail. It was here that the German strategic theory contrasted so violently with the French. The Germans maintained that an ordeal which Napoleon might have been able to live through with his veterans and after fifteen years of successful war, a modern conscript army, most of its men just taken from civilian life and all of short service, would never endure. They believed the operative corner would go to pieces and either be pounded to disintegration, or outflanked, turned, and caught in the first days of the shock before the rest of the square had time to "work." The French believed the operative corner would stand the shock, and, though losing heavily, would remain in being. They believed that the operative corner of the square would, even under modern short service and large quasi-civilian reserve conditions, remain an army. They staked their whole campaign upon that thesis, and they turned out to be right. But they only just barely won through, and by the very narrowest margin. Proving right as they did, however, the success of their strategical theory changed the whole course of the war. With this contrast of the great opposing theories considered, I come to the conclusion of my Second Part, which examines the forces opposed. I will now turn to the Third Part of my book, which concerns the first actual operations from the Austrian note to the Battle of the Marne. FOOTNOTES: