There were several factors. In the case of Central Asia, the Abbasid Dynasty spread Islam as it grew its empire. The Abbasid Caliphs were actually extremely tolerant of the non-Muslims (whom they referred to as dhimmi) in their empire, however, all non-Muslims were required to pay a special tax known as Jizya. Many simply chose to convert to avoid paying the tax.

In West Africa, the spread of Islam can largely be attributed to the Mali Emperor Mansa Musa (North Africa had already been converted to Islam by the Umayyads and Abbasid dynasties). Musa was fabulously wealthy from the rich gold deposits in West Africa, and when he went on a pilgrimage to Mecca in 1324, he flaunted his wealth along the way. Musa brought back to his court numerous Islamic scholars and judges, which allowed the city of Timbuktu to become an epicenter of Islamic learning. The fact of the matter is though, many indigenous West Africans chose to maintain their traditional religion, and those who converted to Islam syncretized elements of indigenous religions into the Arab faith (For an interesting account of this, read Ibn Battuta's journals).

In Oceania, Conversion to Islam was caused by trade and missionaries. Arab and other Muslim merchants sailed to Oceania for trade purposes and some settled there. Indigenous traders recognized the advantages of converting to Islam, and so many chose to so. In addition, Sufi missionaries were crucial in the spread of Islam. Sufis can best be compared to the Jesuits, as they were known for enforcing belief over orthodoxy. Sufis, who were known to be extremely kind and humble, welcomed native peoples to incorporate elements of their own religions into Islam. the result was a unique syncretized Islam that grew throughout Oceania.