The expansion of the Arab Empire in the years following the Prophet Muhammad's death led to the creation of caliphates, occupying a vast geographical area and conversion to Islam was boosted by missionary activities particularly those of Imams, who easily intermingled with local populace to propagate the religious teachings. These early caliphates, coupled with Muslim economics and trading and the later expansion of the Ottoman Empire, resulted in Islam's spread outwards from Mecca towards both the Atlantic and Pacific Oceans and the creation of the Muslim world. Trading played an important role in the spread of Islam in several parts of the world, notably southeast Asia.