Islam is Brunei's national religion. Sixty-five percent of the population is Muslim, mostly Sunnis of Malay origin who follow the Shafii school of Islamic law. Most other Muslims are Kedayans (converts from indigenous tribal groups) and Chinese converts. Islam was adopted in the fifteenth century when a Malay Muslim was installed as sultan. The sultan traditionally was responsible for upholding the Islamic way of life, although the responsibility usually was delegated to appointed officials. Since the 1930s sultans have used rising oil revenues to provide an extensive social welfare system and promote Islam, including subsidizing the hajj, building mosques, and expanding the Department of Religious Affairs. The current sultan promotes the Malay Islamic monarchy as a national ideological alternative to Islamic theocracy.