With the Great Arab Revolt in 1916 and the consequent British invasion, the area came under the Anglo-Arab ruled Occupied Enemy Territory Administration East in 1917, which was declared as the Arab Kingdom of Syria in 1920. Following the French occupation of only the northern part of the Syrian Kingdom, Transjordan was left in a period of interregnum. A few months later, Abdullah, the second son of Sharif Hussein, arrived in Transjordan. With the Transjordan memorandum to the British Mandate for Palestine in the early 1920s, it became the Emirate of Transjordan under the Hashemite Emir. In 1946, independent Hashemite Kingdom of Transjordan was formed and shortly admitted to the United Nations and the Arab League. In 1948, Jordan fought with the newly born state of Israel over lands of former Mandatory Palestine, effectively gaining control of the West Bank and annexing it with its Palestinian population. Jordan lost the West Bank in the 1967 War with Israel, and since became the central base of the Palestine Liberation Organization (PLO) in its struggle against Israel. The alliance between the PLO and the Jordanians, active during the War of Attrition, came to an end in the bloody Black September in Jordan in 1970, when a civil war between Jordanians and Palestinians (with Syrian Ba'athist support) took thousands of lives. In the aftermath, the defeated PLO was forced out of Jordan together with tens of thousands of its fighters and their Palestinian families, relocating to South Lebanon.