Which two factors contributed to the spread of islam in africa?

The Islamic empire extended into North Africa.

The gold-salt trade brought Islamic Arabs into western and southern Africa.

The Islamic empire extended into the North Africa.

For Islam: (monotheistic religion):

Holy land: the Ka'bah is the most sacred of all sites in Islam because it is considered the house of Allah (God). 
Other monotheistic faiths: In Islam, we believe that all of the monotheistic religions are "religions of the book" because they were all mentioned in the Qur'an (holy book).
Holy Book: Qur'an. It tells stories similar to those of Judaism and Christianity, such as Noah's Arc, Adam and Eve, Moses and the Pharaoh, etc. The difference, however, is that the Qur'an places emphasis on some stories rather than others. Also, there are noticeable differences between some of the stories between different religions.
Differences and Divisions: There are many different sects of Islam, for example: Sunni, Shia, Sufi, etc. 
Shared Basic Beliefs: each religion has a place of worship and prayers, believes in one God, prophets, and sin, etc. The list goes on...
Basic Beliefs of Islam: in islam, the Five Pillars of Islam are the most basic beliefs: Shahadah (declaration of faith), Salat (five prayers per day), Sawm (fasting during designated dates), Zakat (charity), and Hajj (pilgrimage to Mecca).