Final answer:
Islam spread primarily through trade, which facilitated social interactions and cultural exchanges along extensive networks, and through military conquests, which incorporated new regions into Islamic empires.
Step-by-step explanation:
The two primary ways that Islam spread were through trade and military conquest. Trade networks extended from West Africa to China, and these were crucial in facilitating the spread of Islam. Traders shared a common language, Arabic, and engaged with local populations through social interactions such as intermarriage, thus helping to further disseminate Islamic beliefs and practices. Military conquests also played a significant role, as the expanding Islamic empires brought new territories under Muslim political and cultural influence, which often included the spread of Islam. Over time, local adopters of Islam would sometimes blend newly introduced Islamic practices with their indigenous traditions, leading to a geographically and culturally diverse Muslim world.