an waters. Haig was not formally subordinate to Joffre but the British played a lesser role on the Western Front and complied with French strategy. In January 1916, Joffre had agreed to the BEF making its main effort in Flanders, but in February 1916 it was decided to mount a combined offensive where the French and British armies met, astride the Somme River in Picardy before the British offensive in Flanders. A week later the Germans began an offensive against the French at Verdun. The costly defence of Verdun forced the French army to commit divisions intended for the Somme offensive, eventually reducing the French contribution to 13 divisions in the Sixth Army, against 20 British divisions. By 31 May, the ambitious Franco-British plan for a decisive victory, had been reduced to a limited offensive to relieve pressure on the French at Verdun with a battle of attrition on the Somme.
The Chief of the German General Staff, Erich von Falkenhayn, intended to end the war by splitting the Anglo-French Entente in 1916, before its material superiority became unbeatable. Falkenhayn planned to defeat the large amount of reserves which the Entente could move into the path of a breakthrough, by threatening a sensitive point close to the existing front line and provoking the French into counter-attacking German positions. Falkenhayn chose to attack towards Verdun to take the Meuse heights and make the city untenable. The French would have to conduct a counter-offensive on ground dominated by the German army and ringed with masses of heavy artillery, leading to huge losses and bring the French army close to collapse. The British would then have to begin a hasty relief offensive and would also suffer huge losses. Falkenhayn expected the relief offensive to fall south of Arras against the Sixth Army and be destroyed.[Note 1] If such Franco-British defeats were not enough, Germany would attack the remnants of both armies and end the western alliance for good. The unexpected length of the Verdun offensive and the need to replace many exhausted units at Verdun, depleted the German strategic reserve placed behind the Sixth Army, which held the Western Front from Hannescamps, 18 kilometres (11 mi) south-west of Arras to St. Eloi, south of Ypres and reduced the German counter-offensive strategy north of the Somme, to one of passive and unyielding defence.
Battle of Verdun
The Battle of Verdun (21 February–18 December 1916) began a week after Joffre and Haig agreed to mount an offensive on the Somme. The German offensive at Verdun was intended to threaten the capture of the city and induce the French to fight an attritional battle, in which German advantages of terrain and firepower would cause the French disproportionate casualties. The battle changed the nature of the offensive on the Somme, as French divisions were diverted to Verdun, and the main effort by the French diminished to a supporting attack for the British. German overestimation of the cost of Verdun to the French contributed to the concentration of German infantry and guns on the north bank of the Somme. By May, Joffre and Haig had changed their expectations of an offensive on the Somme, from a decisive battle to a hope that it would relieve Verdun and keep German divisions in France, which would assist the Russian armies conducting the Brusilov Offensive. The German offensive at Verdun was suspended in July, and troops, guns, and ammunition were transferred to Picardy, leading to a similar transfer of the French Tenth Army to the Somme front. Later in the year, the Franco-British were able to attack on the Somme and at Verdun sequentially and the French recovered much of the ground lost on the east bank of the Meuse in October and December.
The Brusilov Offensive (4 June–20 September), absorbed the extra forces that had been requested on 2 June by General von Below, the Second Army commander, for a spoiling attack on the Somme. On 4 June, Russian armies attacked on a 200-mile (320 km) front, from the Rumanian frontier to Pinsk and eventually advanced 150 kilometres (93 mi), re