region, central Saudi Arabia, comprising a mainly rocky plateau sloping eastward from the mountains of the Hejaz. On the northern, eastern, and southern sides, it is bounded by the sand deserts of an-Nafūd, ad-Dahnāʾ, and the Rubʿ al-Khali. It is sparsely settled, except for the fertile oases strung along the escarpment of Jabal (mountains) Ṭuwayq and the al-ʿAramah plateau. The arid region remained politically divided among rival peoples until the mid-18th century, when it became the centre of the Wahhābī, a fundamentalist Islāmic movement. Led by the Muslim scholar Muḥammad ibn ʿAbd al-Wahhāb and the Āl Saʿūd family, the movement consolidated Najd and expanded into Mecca in 1803. This expansionist policy antagonized the Ottomans, who seized the provincial capital of ad-Dirʿīyah. The Āl Saʿūd, however, quickly regained control, and, with Riyadh as the new capital from 1824, the dynasty has ruled Najd continuously, save for a brief period around the turn of the century when the Rashīd dynasty extended its power over the province. Ibn Saʿūd proclaimed the unified Kingdom of Saudi Arabia in 1932, and his provincial capital of Riyadh became the national capital, although Jidda continued as the diplomatic capital. Oases groups within Najd region include al-Kharj, al-Maḥmal, as-Sudayr, al-Washm, al-ʿĀriḍ, al-Qaṣīm, and Jabal Shammar.