During the First World War, Turkey became a German ally and its empire collapsed when British forces invaded Mesopotamia in 1917 and occupied Baghdad.
At the Paris Peace Conference in 1919, the group of the of the victorious nations in World War I (the allies) made Iraq, which constituted the former Ottoman states (Wilayat) of Mosul, Baghdad, and Al Basrah) under the British mandate. According to the mandate system system, a territory that had formerly been held by either Germany or the Ottoman Empire was placed nominally under the supervision of the League of Nations with the administration of the mandate given to one of the First World War victorious allied counties, including Britain and France, until the territory is able to govern itself. Iraq was classified as Class A mandates; such types of mandates were expected to achieve independence in a few years.
The creation of the British Mandate in Iraq was officially confirmed at the Allied governments’ conference in San Remo, Italy, in April 1920. When the Iraqi Arabs learned of this decision in July 1920, they began an armed uprising against the British, whose senior administrator in Iraq drafted a plan for a provisional government of the new state of Iraq. According to the plan in question, Iraq was to be a kingdom with a government directed by a council of Arab ministers under the supervision of a British high commissioner. An invitation to rule the news state of Iraq was offered in August 1921 to Faisal, was elected King of Iraq by a plebiscite in August 1921 winning 96% of the votes.
Full independence of Iraq was not achieved until 1932, when the British Mandate was officially terminated. Iraq joined the League of Nations in the October of that year, and was officially recognized as an independent sovereign state. On Faisal's death in 1933, he was succeeded by his son, King Ghazi I.