During the First World War, an Arab Revolt, supported by Britain, succeeded in removing the Ottomans from the Arabian peninsula; in the period following this Ibn Saud managed to expand his kingdom considerably, eventually proclaiming the Kingdom of Saudi Arabia in 1932. In the south-west the Idrisid Emirate of Asir had taken advantage of the Ottoman withdrawal and declared independence in 1917, only to be annexed by the Saudis in 1926–30. More successful was the Mutawakkilite Kingdom of Yemen (later known as the Yemen Arab Republic or North Yemen) further south, which declared independence in 1918. North Yemen and Saudi Arabia had no defined frontier and disputed ownership of border territories (notably Asir, Jizan and Najran, claimed by North Yemen as part of 'Greater Yemen'); these tensions culminated in a border war in 1934, in which Saudi Arabia won control over most of the disputed territories. By the Treaty of Taif, signed 12 May 1934, a partial border was drawn that extended inland to the vicinity of Najran, being demarcated on the ground in the following two years. This treaty was renewable every 20 years.