The main aim of this book is to answer the following question: how does one account for the speed with which the Arab empire was built? The period covered extends from the rise of Islam down to the middle of the eighth century.
Why would a hardened band of foreign jihādi warriors agree to work for a self-proclaimed leader of the Christian world – especially one militantly opposed to Islam, who kept his own Muslim citizens under close surveillance? And why would such a ruler choose to keep that particular type of professional killer in his personal employ?
Despite their presence in the popular imagination and their undoubted importance in the narrative of medieval history, the Crusades have for a long time sat apart from mainstream medieval historiography. Traditionally, the Crusades themselves are as peripheral in the minds of historians of Europe as they were geographically.