Final answer:
The religion of Islam spread into central and southwestern Asia through military conquest, trade, migration, intermarriage, and missionary work. It also expanded through the establishment of caliphates and conversion of ruling elites in sub-Saharan Africa.
Step-by-step explanation:
The religion of Islam spread into central and southwestern Asia through a combination of military conquest, trade, migration, Sufi missionary work, and intermarriage. In the seventh and eighth centuries, Muslim forces advanced eastward and conquered regions including modern-day Pakistan. Islam also spread through trade networks, especially along the trans-Saharan trade routes, and created a network of believers who trusted each other due to shared language and customs. Additionally, the religion expanded through the establishment of caliphates and the conversion of ruling elites in sub-Saharan Africa.