After Muhammad's death in 632 CE, his Medinan companions debated which of them should succeed him in running the affairs of the Muslims while Muhammad's household was busy with his burial. Umar and Abu Ubaidah ibn al-Jarrah pledged their loyalty to Abu Bakr, with the Ansar and the Quraysh soon following suit. Abu Bakr thus became the first "Khalīfaṫu Rasūli l-Lāh" (, "Successor of the Messenger of God"), or Caliph, and embarked on campaigns to propagate Islam. First he would have to subdue the Arabian tribes which had claimed that although they pledged allegiance to Muhammad and accepted Islam, they owed nothing to Abu Bakr. As a caliph, Abu Bakr was not a monarch and never claimed such a title; nor did any of his three successors. Rather, their election and leadership were based upon merit.