Final answer:
Islam spread quickly after the death of Muhammad through military conquests, trade networks, and social and religious practices that facilitated a unified Islamic community. The decline of regional empires and the establishment of consistent legal and market systems also played significant roles.
Step-by-step explanation:
After the death of Muhammad in 632 CE, Islam spread quickly through a combination of factors. These included military conquests by subsequent Muslim rulers, which expanded the ummah into vast territories; peaceful missionary work and the establishment of Islamic institutions, which unified Muslims across different regions; and extensive trade networks, bolstered by a common language and shared values, which facilitated the spread of Islamic customs and practices.
The early Muslim community faced significant challenges after Muhammad's demise, such as leadership succession and maintaining unity. Despite these challenges, the spread of Islam was further accelerated by intermarriage and the influence of religious scholars and leaders, which helped to diffuse the religion both spatially and culturally. The decline of the Roman and Persian Empires also created a vacuum that Islam was well-positioned to fill, politically and spiritually.
Equally important were the social interactions engendered by trade and travel. Markets across the Islamic world operated under a consistent legal system, and traders spread the faith along trans-Saharan routes and into various empires and kingdoms. This vast network of believers created a cohesive community, even though they were spread across different geographic and political landscapes. Ultimately, Islam's growth was a multifaceted phenomenon that cannot be attributed to a single cause but rather a myriad of interlinked social, economic, and political factors.