Throughout the book, Armstrong contextualizes Islam’s history and culture by emphasizing how it has interacted with other religious traditions, including Christianity, Hinduism, and the pre-Islamic pagan traditions of the Arabian Peninsula. The other Abrahamic faiths, Judaism and Christianity, were particularly important to Muhammad’s original formulation of Islam, she writes, because “Muhammad did not think that he was founding a new religion, but that he was merely bringing the old faith in the One God to the Arabs, who had never had a prophet before” (36). Christians and Jews are designated ahl al-kitab (“people of the book”) by Muslims in recognition of their shared scriptural tradition. As noted by Armstrong, Muhammad’s proximity to Jewish communities informed the implementation of several key Muslim practices, such as Friday communal prayer (49). She also asserts that the requirement for Muslim women to wear hair coverings has its origins in Byzantine Christian practice, as early generations of Muslims borrowed this tradition from their Christian neighbors long after the death of Muhammad.

Another important example of external influence on Islam is the evolution of Islamic culture following the Mongol conquests, which Armstrong describes as a “traumatic” event for the whole of Muslim world. Unlike the Jews and Christians, who had a shared sense of history and values with Muslims that informed their interactions with Islamic societies, the Mongol Empire diverged sharply from the Muslim communities it conquered.