Historically there was no clearly defined boundary in this part of the Arabian peninsula; at the start of the 20th century the Ottoman Empire controlled the western coast and Britain the east and south (ruled indirectly via local sheikhs and emirs), with the interior consisting of loosely organised Arab groupings, occasionally forming emirates, most prominent of which was the Emirate of Nejd and Hasa ruled by the al-Saud family.[4] Britain and the Ottoman Empire theoretically divided their realms of influence in Arabia via the so-called 'Blue' and 'Violet lines' in 1913–14, however these agreements were rendered null and void following the collapse of the Ottoman Empire after the First World War.[5][6]