From the 15th of September, 1914, it was clear that the Germans were making a great effort to try and overwhelm the French left. General Joffre parried the attack, reenforcing at first the army of Manoury by an army corps, then transferring to the left of the army of Manoury the entire army of Castelnau that was in Lorraine. A corps of cavalry and four territorial divisions commanded by General Brugère received the order to establish itself on both banks of the Somme and protect the detraining of the army of Castelnau.
From September 21 to September 26, 1914, all the French forces that had newly arrived were engaged in the Lassigny-Reye-Péronne region. They succeeded in withstanding, not without difficulty, the German attack, but they could not advance. The Germans determinedly and unweariedly continued to mass new forces on their right. On the left of the army of Castelnau it was therefore necessary to establish a new army. It was established on September 30, 1914, under the command of General Maud'huy. From the first days of October this army waged violent conflicts in the region of Arras and of Lens. It found facing it two German cavalry corps, the Guard, four active army corps, and two reserve corps.
General Joffre continued without intermission to send new forces to the left. On October 4, 1914, he called on General Foch in the north and charged him with the duty of coordinating the action of all the armies in that region: those of De Castelnau, Maud'huy, and the territorial divisions. At the beginning of October the British army, which was posted on the Aisne, was transferred to the left of the French armies and replaced by the armies of Manoury and d'Espérey. The Belgian army, issuing from Antwerp on October 9, 1914, effected its retreat, covered by the British naval forces and 6,000 French marines. It took its place on the Yser Canal between Nieuport and Dixmude.
The Germans continuing their efforts to turn the French left, it was found necessary again to strengthen that left considerably; and new French army corps were transferred to Flanders and Belgium. It was a new French army that was established and the command of it was intrusted to General d'Urbal. It consisted at first of two divisions of territorials and four divisions of cavalry of the corps of General de Mitry, along with a brigade of naval fusiliers. But from October 27 to November 11, 1914, it received considerable reenforcements.