During the First World War (1914–18), an Arab uprising and the British Empire's Egyptian Expeditionary Force under General Edmund Allenby drove the Turks out of the Levant during the Sinai and Palestine Campaign. The United Kingdom had agreed in the McMahon–Hussein Correspondence that it would honour Arab independence if they revolted against the Ottomans, but the two sides had different interpretations of this agreement, and in the end the UK and France divided up the area under the Sykes–Picot Agreement—an act of betrayal in the eyes of the Arabs. Further complicating the issue was the Balfour Declaration of 1917, promising British support for a Jewish "national home" in Palestine. At the war's end the British and French set up a joint "Occupied Enemy Territory Administration" in what had been Ottoman Syria. The British achieved legitimacy for their continued control by obtaining a mandate from the League of Nations in June 1922. The formal objective of the League of Nations Mandate system was to administer parts of the defunct Ottoman Empire, which had been in control of the Middle East since the 16th century, "until such time as they are able to stand alone." The civil Mandate administration was formalized with the League of Nations' consent in 1923 under the British Mandate for Palestine, which covered two administrative areas. The land west of the Jordan River, known as Palestine, was under direct British administration until 1948. The land east of the Jordan, a semi-autonomous region known as Transjordan, under the rule of the Hashemite family from the Hijaz, gained independence in 1946.
The divergent tendencies regarding the nature and purpose of the mandate are visible already in the discussions concerning the name for this new entity. According to the Minutes of the Ninth Session of the League of Nations' Permanent Mandate Commission:
Colonel Symes explained that the country was described as "Palestine" by Europeans and as "Falestin" by the Arabs. The Hebrew name for the country was the designation "Land of Israel", and the Government, to meet Jewish wishes, had agreed that the word "Palestine" in Hebrew characters should be followed in all official documents by the initials which stood for that designation. As a set-off to this, certain of the Arab politicians suggested that the country should be called "Southern Syria" in order to emphasise its close relation with another Arab State.
During the British Mandate period the area experienced the ascent of two major nationalist movements, one among the Jews and the other among the Arabs. The competing national interests of the Arab and Jewish populations of Palestine against each other and against the governing British authorities matured into the Arab Revolt of 1936–1939 and the Jewish insurgency in Palestine before culminating in the Civil War of 1947–1948. The aftermath of the Civil War and the consequent 1948 Arab–Israeli War led to the establishment of the 1949 cease-fire agreement, with partition of the former Mandatory Palestine between the newborn state of Israel with a Jewish majority, the Arab West Bank annexed by the Jordanian Kingdom and the Arab All-Palestine Government in the Gaza Strip under the protectorate of Egypt.
Following its occupation by British troops in 1917–1918, Palestine was governed by the Occupied Enemy Territory Administration. In July 1920, the military administration was replaced by a civilian administration headed by a High Commissioner. The first High Commissioner, Herbert Samuel, a Zionist recent cabinet minister, arrived in Palestine on 20 June 1920, to take up his appointment from 1 July.
Following the arrival of the British, Muslim-Christian Associations were established in all the major towns. In 1919 they joined to hold the first Palestine Arab Congress in Jerusalem. Its main platforms were a call for representative government and opposition to the Balfour Declaration.