by another Al-Saud, Abdulaziz Ibn Saud. He gained the support of the Ikhwan, a tribal army inspired by Wahhabism and led by Sultan ibn Bijad and Faisal Al-Dawish, which had grown quickly after its foundation in 1912. With the aid of the Ikhwan, Ibn Saud captured al-Hasa from the Ottoman Empire in 1913. Ibn Saud defeated a rival ruling family and took the title Sultan of Nejd in 1921. By this time the Ottomans had been defeated in World War I, and Ottoman suzerainty and control in Arabia was no more. With the help of the Ikhwan, the Hejaz was conquered in 1924–25. Following this victory however the Ikhwan clashed with Ibn Saud. He opposed their raiding the British protectorates of Transjordan, Iraq and Kuwait, to expand of the Wahhabist realm, and they opposed his policies of allowing some modernization and some non-Muslim foreigners in the country. The Ikhwan were defeated and their leaders executed in 1930 after a two-year struggle. In 1932 the two kingdoms of the Hejaz and Nejd were united as the Kingdom of Saudi Arabia. Era of oil exports Oil was discovered in the Persian Gulf region of Saudi Arabia in 1938, and oil wells eventually revealing the largest source of crude oil in the world. For the king, oil revenues became a crucial source of wealth since he no longer had to rely on receipts from pilgrimages to Mecca. This discovery would alter Middle Eastern political relations forever. During the 1960s and '70s, religious authorities allowed some practices that had previously been forbidden (haram). At the urging of the government and after vigorous debate, religious authorities allowed the use of paper money in 1951, abolished slavery in 1962, permitted the education of females in 1964, and use of television in 1965. By the 1970s, as a result of oil wealth and government modernization policies, economic and social development progressed at an extremely rapid rate, transforming the infrastructure and educational system of the country; in foreign policy, close ties with the US were developed. By 1976 Saudi Arabia had become the largest oil producer in the world. The power of the ulema was in decline. However, in the 1980s and 1990s, this trend was reversed. In 1979, the modernizing monarch of Iran, despite his oil revenues and apparently formidable security apparatus, was overthrown by an Islamic revolution. The new revolutionary Islamic Republic was across the Persian