How did Islam spread from the Arabian Peninsula to reach the borders of three continents, bringing together in an intense brotherhood of faith the nations furthest apart by language, ethnicity, customs, culture, geography or history? How did he so deeply win the hearts of so many once Christian, Zoroastrian, or pagan nations? What were the methods employed by the missionaries of the Prophet's faith, what are the elements of the latter which have so seduced the people, and what are the other factors - socio-cultural, political, economic, religious - that have come into play in this extraordinary historical phenomenon?

These are the questions that Thomas W. Arnold tries to answer in this book, thus proposing what is undoubtedly the first systematic and academic study of the subject carried out by a Western author. In doing so, without encumbering himself with the prejudices current in his time in Europe, he masterfully refuted the theory of "propagation by the sword" - a commonplace of historical thought at the time - by recalling the global tolerance of the powers Muslims, without placing themselves in an apologetic framework and therefore without concealing the episodic persecutions – but while proving that they were the exception and not the rule – nor the influence of other factors, notably political ones.

Beyond the major historical interest of this work in its fair and nuanced presentation of the subject and its desire to clear up myths and clichés, the Muslim reader will also find there, implicitly, a number of spiritual lessons of the first importance and a a near-exhaustive overview of all the diverse communities that make up our marvelous Ummah – the fruit of thirteen centuries of devotion to the cause of Truth by countless believers, from the humblest to the most powerful, who have transmitted it by word and example.