An expeditionary force of the Indian Army landed in Turkish territory at the head of the Persian Gulf almost immediately upon the declaration of war by Britain against Turkey on 5 November 1914. After winning some minor engagements against Turkish forces, it marched into Basra, the chief town of southern Mesopotamia, on the 23rd. The subsequent course of the campaign in Mesopotamia included a number of setbacks for the British. The principal city, Baghdad, was not captured until after nearly two and a half years of fighting, and the chief northern city, Mosul, not indeed until after an armistice had been signed with Turkey. Even so, by the time hostilities ceased, large areas in the south had been under continuous British occupation for four years and the possibility of further advance was throughout the war present in the minds of British leaders, whether in London, Simla or Mesopotamia itself. Against this background of military conquest and a pre-war diplomacy among the European powers, excluding Russia, in which Mesopotamia had been marked out as the British sphere if Turkey was partitioned, it is unsurprising that the political future of the country should have been much discussed within British official circles. War aims went through several phases whose study contributes to understanding of British aims in the war as a whole.