On 23 July the Austro-Hungarian Government sent an ultimatum to Serbia and next day the British Foreign Minister Sir Edward Grey proposed a conference to avert a war and the Belgian Government issued a declaration that Belgium would defend its neutrality "whatever the consequences". No formal provision was made for combined operations with the British Expeditionary Force BEF but joint arrangements had been made and in during the Second Moroccan Crisis, the French had been told that six British divisions could be expected to operate around Maubeuge. French intelligence had obtained a map exercise of the German general staff, in which German troops had gone no further north than Namur and assumed that plans to besiege Belgian forts were a defensive measure against the Belgian army. It was anticipated that the Germans would use reserve troops but also expected that a large German army would be mobilised on the border with Russia, leaving the western army with sufficient troops only to advance through Belgium south of the Meuse and the Sambre rivers. The French deployment was intended to be ready for a German offensive in Lorraine or through Belgium. Since, railway building had given the French General Staff sixteen lines to the German frontier, against thirteen available to the German army and the French could afford to wait until German intentions were clear. Under Plan XVII the French peacetime army was to form five field armies, with a group of reserve divisions attached to each army and a group of reserve divisions on each flank, a military force of c. Divisions from the German army in the west Westheer would be redeployed to the East to deal with the Russians as soon as a breathing-space was gained against the French. A corollary to the emphasis on the Western Front was a lack of troops for the Eastern Front against Russia.
The French would either be annihilated or the manoeuvre from the north would create conditions for victory in the centre or in Lorraine, on the common border. The main German force would still advance through Belgium and attack southwards into France, the French armies would be enveloped on the left and pressed back over the Meuse, Aisne, Somme, Oise, Marne and Seine, by short, rapid attacks, unable to withdraw into central France. Moltke adapted the deployment and concentration plan to accommodate an attack in the centre or an enveloping attack from both flanks as variants, by adding divisions to the left flank opposite the French frontier, from the c. Helmuth von Moltke the Younger succeeded Schlieffen in and was less certain that the French would conform to German assumptions.