MacMahon's correspondence with Sharif Husayn (1915)
In a letter dated the 24th of October, 1915, Sir Henry McMahon, then His Majesty's High Commissioner in Egypt, promises the Sharif of Mecca, Husayn ibn Ali, to "recognise and support the independence of the Arabs within the territories proposed by him." These territories included the Arabian peninsula, Syria (including Lebanon, Palestine, and Transjordan), and Iraq as "purely Arab" areas and part of a future Arab state or states in the region. (See MAP of this area.) Rumors about the content of the Sykes-Picot agreement that were being spread by the Turkish government to cause a rift between Britain and the Arabs were discarded by England as "Turkish war propaganda." After the war, the interpretation of the MacMahon correspondence became contentious because the British insisted that their annexation of Palestine as a direct British mandate and their support of the establishment of a Jewish homeland therein did not constitute a betrayal of its committments to the Arabs since Palestine had not been specifically mentioned. This remained a bone of contention between the British government and Arab representatives arguing for the conversion of Palestine into an Arab state. (See the White Paper of 1939.)
A full version of the correspondence between Sharif Husayn and MacMahon is available on-line at http://www.jewishvirtuallibrary.org/jsource/History/hussmac1.html.
Also see http://www.lib.byu.edu/~rdh/wwi/1916/mcmahon.html.
More background on the Anglo-Arab coalition during the First World War from PASSIA.