The second part of the French plan lay in General Joffre's decision not to do the expected thing. With General Sarrail placed at the extremest point of danger, it would have been a likely move to transfer the entire British Expeditionary Force from the left wing to the weak point at Bar-le-Duc. There is reason to believe that General von Kluck believed that this had been done.
The third part of the defensive prepared by General Joffre was that of a determination to turn the steady retreat into a counterdrive. Time after time had the other generals implored their leader to give them leave to take the offensive, and on every occasion a shake of the head had been the reply. Sir John French had wondered. But when the French officers found themselves in the region of the Marne, close to the marshes of St. Gond, where in 1814 Napoleon had faced the Russians, they were more content. It was familiar as well as historic ground. Even the youngest officer knew every foot of that ground thoroughly. It was, at the same time, the best point for the forward leap and one of the last points at which a halt could be made.
The fourth part of the plan was the holding fast to the point of Verdun, for thereby the communication of the armies of the Central Powers was seriously weakened. It is to be remembered that this actual fighting army of more than a million men depended for food and for ammunition supplies upon the routes from Belgium and Luxemburg by way of Mézières and Montmédy, and the circuitous line to Brussels via St. Quentin. Had Maubeuge fallen a little earlier the situation of the Central Powers would have been less difficult, and both commissariat and ammunition problems would have been easier of solution. But Maubeuge held out until September 7, 1914, and by that time the prime results of the battles of the Marne had been achieved. To this problem Verdun was the key, for from Metz through Verdun ran the main line, less than one-half the length of line to the Belgian bases of supplies, and, owing to the nature of the country, a line that could be held with a quarter the number of men. But Verdun stood, and General Joffre held the two armies back to back, converging on the point at Verdun.