"Transjordan" was a word coined to express the idea that the lands so described were "across the Jordan", i.e. on the far (eastern) side of the Jordan River. On the western side of the Jordan River lie Israel and the West Bank, which contain many places of historical and religious signifance to Judaism, Christianity, and Islam.
Under the Ottoman empire, Transjordan did not correspond precisely to a political division, though most of it belonged to the Vilayet of Sam. The inhabitants of northern Jordan had traditionally associated with Syria, those of southern Jordan with the Arabian Peninsula, and those of western Jordan with the Arabs of Palestine. Historically the territory had formed part of various empires; among these are the Assyrian, Achaemenid, Macedonian (Seleucid), Nabataean, Ptolemaic, Roman, Sassanid, Muslim, Crusader, and Ottoman empires.
Previously a part of the territory covered by the planned League of Nations mandate for Palestine, Transjordan was created as a separate administrative entity on April 11, 1921 to provide a throne of sorts (albeit one under British control) for the Hashemite Emir Abdullah, elder son of Britain's wartime Arab ally Sharif Hussein of Mecca. The move also excluded the land east of the Jordan from Britain's wartime undertaking in the Balfour Declaration (2 November 1917) to support the creation in Palestine of a Jewish national home.
Britain recognized Transjordan as a state on May 15, 1923 and gradually relinquished control, limiting its oversight to financial and foreign policy matters. In March 1946, under the Treaty of London, Transjordan became a kingdom and on May 25, 1946, the parliament of Transjordan proclaimed the emir king, and formally changed the name of the country from the Emirate of Transjordan to the Hashemite Kingdom of Transjordan. In December 1948, Abdullah took the title King of Jordan, and he officially changed the country's name to the Hashemite Kingdom of Jordan in April 1949. The following year he annexed the West Bank. The coinage, Cisjordan, meant to apply specifically to the West Bank at that time, has not since caught on, outside Jordanian circles.