Under the leadership of Sir Sultan Mahomed Shah, Aga Khan III, the first half of the 20th century was a period of significant development for the Ismā'īlī community. Numerous institutions for social and economic development were established in the Indian Subcontinent and in East Africa. Ismailis have marked the Jubilees of their Imāms with public celebrations, which are symbolic affirmations of the ties that link the Ismāʿīlī Imām and his followers. Although the Jubilees have no religious significance, they serve to reaffirm the Imamat's worldwide commitment to the improvement of the quality of human life, especially in the developing countries.