In a little over 100 years after the death of the prophet Muhammad in 632, Arab Muslims controlled an empire that reached out from Medina and Mecca as far west to what is now Morocco and as far east to what is now Afghanistan. They brought Arabic and the new Muslim religion to diverse places where there were previously no Arab-speakers. Just how and why that happened is the subject of Hugh Kennedy’s ambitious and highly annotated The Great Arab Conquests: How the Spread of Islam Changed the World We Live In.

Kennedy structures the book geographically and somewhat chronologically, describing the conquests of each region as they happened by the Arab Muslims who led the campaigns. He notes that large empires had been created more quickly, as in the cases of Alexander the Great and Genghis Khan, but tells us what was so different, in this case.

What makes the Arab Muslim conquests so remarkable is the permanence of the effect they had on the language and religion of the conquered lands. Spain and Portugal are the only countries conquered at this time where the spread of Islam has been reversed; by contrast we now think of Egypt as a major centre of Arab culture and of Iran as a stronghold of militant Islam.  At the time of conquest, Egypt was a Greek and Coptic-speaking Christian region, while what is now Iran was a Pahlavi-speaking region made up largely of Christians with a Zoroastrian ruling class.

The Arab Muslims first conquests were in Syria and Palestine. The Byzantine Empire they encountered there and elsewhere around the Mediterranean Seas was a faint shadow of the Roman Empire in the days of emperors like Augustus, Marcus Aurelius, and Hadrian. It was an empire much weakened by a bubonic plague that had occurred during the 6th century (significantly reducing the population), wars with the Sasanian Empire (based in what is now Iraq and Iran) that had strained the military, conflicts among Christian sects (such as the Coptics in Egypt versus the Constantinople-sanctioned Chalcedonian church), and, in the case of the Iberian peninsula, controlled by a divided Visigothic kingdom. In many cases the great old Byzantine cities such as Antioch and Carthage fell easily to the Muslims because there was hardly anyone living in them.

The Muslims were relatively open-minded conquerors who did not require the conquered to convert to the new faith or change their language. They collected an annual tribute in exchange for those rights. At first, it was only the ruling class of Arabs who spoke and administered in Arabic. The conversion to Islam and the adoption of Arabic amongst the general population would take another two- to three-hundred years.

Kennedy’s sources are the primary ones, drawn largely from the Muslim sources and, when available, from the conquered. There is a lot of repetition in the text concerning Muslim sources around three points: there is no coherent account of a given battle other than anecdotes that extol the “warlike puritanism” of the Muslims and the decadence of their opponents, the Muslim accounts copiously recorded the distribution of the war booty, and that the Muslims often preferred negotiating a settlement that allowed the conquered to practice their religion and retain their language as long as they paid an annual tribute to the conquerors. These points are belabored over and over.

Between this belaboring and the endless parade of names (some significant, some not) makes for something more akin to a dry factual textbook than an engrossing narrative of popular history. It is far too fact-heavy and laden with countless details for most readers. There is mention here and there about internal violent struggles for power between factions determining the succession of caliphs. But there are no explanations of those struggles, or even a clear delineation of who was directing the new empire at the top when new lands were being acquired.

It is confusing at times, trying to keep track of all the Muslim leaders, who they fought, where they fought, when they fought, and who they appointed to what leadership post. You’re reading about Walid in the chapter on the Conquest of Iraq when you say to yourself, “Wait a minute. Wasn’t he the one who helped conquer Syria, including the city of Damascus?” You are correct. And then a few pages later Kennedy tells you that Walid was ordered to Syria.

Kennedy does a highly admirable job of collecting what is known about the Muslim Conquest in the religion’s first century and attempting to put it into one all-encompassing tome. Few people seem up to this important task, much fewer able to pull it off. It is a much-needed guide for the English-speaking world to how the Muslim faith was initially spread, bringing changes that are still shaping our world today.

Serious students of history will find much of value. Kennedy’s achievement is quite impressive; the summarizing of numerous dubious and contradictory accounts about the first century of the Muslim religion’s spread into a single volume. For the casual reader interested in how and why the Muslim religion spread so rapidly after the death of its founder, there is too much information and too little perspective.