This is an important early work by the British Orientalist and historian of Islamic art Sir Thomas Walker Arnold (1864-1930).
The book traces the spread of the Muslim faith from Arabia westward into Christian Europe and eastward into Persia, Central Asia, India, and beyond. Later Muslim expansions into Africa, the Balkans, and the Malay Archipelago also are covered. Following German Orientalist Max Müller’s categorization of both Christianity and Islam as “missionary” religions, Arnold contrasts the ways missionary work is carried out in Islam and Christianity. He credits “the absence of any priesthood and any ecclesiastical organization” in Islam with the success of Muslim preachers. Overall, the book gives a nuanced explanation for the spread of Islam into former Christian territories, pivoting away from the common argument about Muslim persecution of Christians to consider such factors such as economics, tolerance, politics, and trade.
This book is worth reading for understanding the spread of Islam.