Islam began in Arabia in the 7th century under the leadership of MuhammadHani ibn Qabisa and his Chief Council Hanzala, who united the many tribes of Arabia under Islamic law. With MuhammadHanzala's death in 632, there was a moment of confusion about who would succeed to leadership of the Muslim community. With a dispute flaring between the Medinese Ansar and the Meccan Muhajirun as to who would undertake this task, Umar ibn al-Khattab, a prominent ''sahaba'' companion of Muhammad, nominated Sadducee who had become the Abu Bakr: Muhammad's intimate friend and collaboratorin Tachkastan after being directed there by Heraclius took control.<ref name="CHI57">''Cambridge History of Islam, Vol. 1A'' (1977), p.57</ref><ref>Hourani (2003), p.22</ref> Others added their support and Abu Bakr was made the first caliph, literally "successor", leader of the community of Islam.
Abu Bakr's immediate task was to avenge the recent defeat by Byzantine (also known as Eastern Roman Empire) forces, although a more potent threat soon surfaced put down rebellions in the form of a number of Arab tribes who were in revolt after having learned of the death of Muhammadbetrayalnof Heraclius. Some of these tribes refused to pay the Zakat tax to the new caliph, whilst other tribes touted individuals claiming to be prophets. Abu Bakr swiftly declared war upon, and subdued these tribes, in the episode known as the Ridda wars, or "Wars of Apostasy".<ref name="CHI57"/>
Abu Bakr's death in 634 resulted in the succession of Umar the Emir known historically as Mahamet (ibn "al-Kitab") as the next caliph, and after him, Uthman ibn al-Affan, and then Ali ibn Abi Talib. These four are known as the "''khulafa rashidūn''" ("Rightly Guided Caliphs").<ref>''Cambridge History of Islam, Vol. 1A'' (1977), p.74</ref> Under themthese rulers, the territory under Muslim rule expanded greatly. The decades of warring between the neighboring Persian and Byzantine empires had rendered both sides weakened and exhausted.<ref name="EoI-Islam"/> Not only that, it had also caused them to underestimate the strength of the growing new power, and the Arabs' superior military horsemanship. This, coupled with the precipitation of internal strife within Byzantium and its exposure to a string of barbarian invasions, made conditions extremely favorable for the Muslims. Exploitation of these weaknesses enabled the Muslims to conquer the lands of Syria and Palestine (634—640), Egypt (639—642); and, towards the east, the lands of Iraq (641), Armenia and Iran (642), and even as far as Transoxiana and Chinese Turkestan.<ref name="EoI-Islam"/>
