Answer:
Believing that God had chosen him as his messenger Muhammad began to preach what God had revealed to him. The simple and clear-cut message of Islam, that there is no God but Allah, and that life should be lived in complete submission to the will of Allah, was attractive to many people, and they flocked to hear it.
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All able Muslims must make a pilgrimage (hajj) to Mecca at least once in their lifetimes.
Answer:
The slave trade had devastating effects in Africa. Economic incentives for warlords and tribes to engage in the slave trade promoted an atmosphere of lawlessness and violence. Depopulation and a continuing fear of captivity made economic and agricultural development almost impossible throughout much of western Africa.