Final answer:
Islam spread quickly through familiar religious institutions, conquests, and trade along trans-Saharan routes.
Step-by-step explanation:
The rapid spread of Islam can be attributed to several factors. First, the Muslim community established familiar religious institutions in new communities, providing consistency and facilitating movement within the Islamic world. Second, early expansion occurred through conquests, expanding the ummah into new territories. Third, trade and social bonds along trans-Saharan trade routes allowed for the gradual spread of Islam.