Rashidun Empire
After Muhammad's death in 632, the Medinan Ansar were debating who -among them- should succeed prophet Muhammad in running the affairs of the Muslims.  They chose Abu Bakr. So he became the first Khalifa Rasul Allah (Successor of the Messenger of God), and started a campaigns to for the Muslim Religion. At first he  the Arabian tribes which had left the Islamic community. As a Khalifa or Caliph he was not a monarch and never claimed such a title. His three successors also never claimed a title as monarch.