text: Background At the beginning of 1917, the British and French were still searching for a way to achieve a strategic breakthrough on the Western Front. The previous year had been marked by the costly success of the Anglo-French offensive astride the River Somme, while the French had been unable to take the initiative because of intense German pressure at Verdun until after August 1916. The battles consumed enormous quantities of resources while achieving virtually no strategic gains on the battlefield. The cost to Germany of containing the Anglo-French attacks had been enormous and given that the material preponderance of the Entente and its allies could only be expected to increase in 1917, Field Marshal Paul von Hindenburg and General Erich Ludendorff decided on a defensive strategy on the Western Front for that year. This impasse reinforced the French and British commanders' belief that to end the stalemate they needed a breakthrough; while this desire may have been the main impetus behind the offensive, the timing and location were influenced by political and tactical considerations.
  Home fronts
  The mid-war years were momentous times. Governing politicians in Paris and London were under great pressure from the press, the people and their parliaments to win the war. Hundreds of thousands of casualties had been suffered at the battles of Gallipoli, the Somme and Verdun, with little prospect of victory in sight. The British Prime Minister, H. H. Asquith, resigned in early December 1916 and was succeeded by David Lloyd George. In France, Prime Minister Aristide Briand, along with Minister of Defence Hubert Lyautey were politically diminished and resigned in March 1917, following disagreements over the prospective Nivelle Offensive. The United States was close to declaring war on Germany; American public opinion was growing increasingly incensed by U-boat attacks upon civilian shipping, which had begun with the sinking of  in 1915 and culminated in the torpedoing of seven American merchantmen in early 1917. The United States Congress declared war on Imperial Germany on 6 April 1917 but it would be more than a year before a suitable army could be raised, trained and transported to France.