In 1913 Britain had acquired the Abadan oil field of Persia, and with the advent of WWI it was concerned to protect both the oil fields and the route to India. When the Ottoman Turks joined the war in October 1914 British and Indian troops occupied Basra in Mesopotamia. They began to advance towards Baghdad, but were halted at Kut-al-Amara. General Maude captured Kut in February 1917, entering Baghdad on 11th March. One contingent of British troops reached the oil fields of Baku in May 1918, which it occupied until September, when the Turks reoccupied it. A further contingent moved to capture Ramadi in September 1917 and another to capture Tikrit in July 1918, before advancing on Mosul. Meanwhile from Egypt General Allenby was advancing north into Palestine, aided by Arab partisans organized and led by T. E. Lawrence. (Lawrence of Arabia). In December 1917 Jerusalem was occupied, from where Allenby moved north towards Damascus in October 1918. After the armistice of Mudros on 30th October, British troops briefly reoccupied Baku from November 1918 until August 1919 aiming to deprive the Bolsheviks (after the Russian Revolution of 1917) of its oil. Britain had now occupied all Mesopotamia, and considered the possibility of creating a single British dominion of Mesopotamia, consisting of Palestine, and the present day areas of Jordan, Iraq, and parts of Iran.
After WWI Britain was given control of Palestine, Transjordan and Mesopotamia by mandate from the League of Nations.

Under the British Mandate from the League of Nations, Ahd Allah Faisal, son of Hussein was recognized as King Faisal in 1921. On 3rd October 1932 independence was granted and Britain's influence remained strong until the overthrow of the monarchy in 1958.