The famous German scientist, author of many works on theology, professor at the University of Gottingen presented the history of the Arab Caliphate - a once huge and powerful empire. Noting the inextricable connection of the political, religious and administrative power of the Arab Caliphate, the author analyzes the history of the emergence of Islam, its development, features and commonality with other major world religions. Tells how rulers came to power and died; when the governors of the most important provinces took office and retired; who the caliphs appointed to lead the Hajj each year and how the campaigns of conquest took place. In his research, Wellhausen relied on original sources - examples of ancient Arab historical literature, Kufi and Medina legends. Among the cited authors are such authorities as Abu Mikhnaf, At-Tabari, Ibn Ishaq, Abu Mashar, al-Waqidi.