Plan German strategy had given priority to offensive operations against France and a defensive posture against Russia since 1891. German planning was determined by numerical inferiority, the speed of mobilisation and concentration and the effect of the vast increase of the power of modern weapons. Frontal attacks were expected to be costly and protracted, leading to limited success, particularly after the French and Russians modernised their fortifications on the frontiers with Germany. Alfred von Schlieffen, Chief of the Imperial German General Staff, (OHL) from devised plans to evade the French frontier fortifications with an offensive on the flank, which would have a local numerical superiority and obtain rapidly a decisive victory. By 1906 such a manoeuvre was intended to pass through neutral Belgium and threaten Paris from the north. Helmuth von Moltke the Younger succeeded Schlieffen in 1906 and was less certain that the French would conform to German assumptions. Moltke adapted the deployment and concentration plan, to accommodate an attack in the centre or an enveloping attack from both flanks as variants to the plan, by adding divisions to the left flank opposite the French frontier, from the expected to be mobilised in the (western army). 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, unable to withdraw into central France. Either the French would be annihilated or the manoeuvre from the north would create conditions for victory in the centre or in Lorraine on the common border. Battle of the Frontiers, 7 August – 13 September The Battle of the Frontiers is a general name for all of the operations of the French armies until the Battle of the Marne. A series of encounter battles began between the German, French and Belgian armies, on the German-French frontier and in southern Belgium on 4 August 1914. The Battle of Mulhouse (Battle of Alsace ) was the first French offensive against Germany. The French captured Mulhouse until forced out by a German counter-attack on 11 August and fell back toward Belfort. The main French offensive, the Battle of Lorraine , began with the Battles of Morhange and Sarrebourg () advances by the First Army on Sarrebourg and the Second Army towards Morhange. Château-Salins near Morhange was captured on 17 August and Sarrebourg the next