Complex sentence: An alliance of the House of Saud and the Wahhabi movement, known as the Emirate of Diriyah carried out the first demolition and the Sultanate of Nejd, also ruled by the House of Saud, carried out the second.
Split into simpler sentences: An alliance of the House of Saud and the followers of the Wahhabi movement, known as the Emirate of Diriyah carried out the first demolition. The Sultanate of Nejd, also ruled by the House of Saud and followers of Wahhabism, carried out the second.