Islam spread rapidly in the millennium following Mohammed’s death in 632 CE, reaching parts of what is today Western Europe by just 750 CE. Mohammed’s rule was initially followed by four successors who came to be known as the “Rashidun” or the “Rightly Guided Caliphs.” These leaders began the spread Islam as it happened in three primary ways: military conquests, trade, and religious missionaries.

Islamic expansion throughout North Africa and the Middle East, in places such as Egypt and Persia, was primarily carried out through Arab Muslim armies. Arab nomads violently conquered many territories that used to be under Byzantine control. Many of the Arabs fighting to conquer Byzantine territories were successful because they had previously served in Byzantine armies and could anticipate their opponents’ strategies. This period was thus one of intense turmoil for the Byzantines. Their land was being conquered and damaged, their population was shrinking from attacks and conversions, and the armies' travels led to the spread of diseases. Overall, as the Islamic empire expanded and flourished, the Byzantines lost a great deal of power.

In the region of the Indian Ocean, Islam spread mostly through trade, as this area was already a popular international trading hub. Muslim merchants brought a new style to the trading world because they had their own set of strict yet peaceful rules. Their approach to trade ensured fair and nonviolent exchanges that other merchants from around the world favored. This motivated many non-Muslims to convert to Islam, because it was easier to communicate and trade with people who practiced the same religion.

Before Islamic expansion the Byzantines had been profiting off these Indian Ocean trade routes. The success the Muslim merchants and missionaries had in this region thus led to more economic problems for the Byzantines.

After the Rashidun Caliphs, Islamic power became dynastic. The following Umayyad and Abbasid caliphates centralized the power of the expanding empire, giving it more structured political influence throughout the world.