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Abu Bakr was succeeded by Umar, his appointed successor from the Banu Adi clan, who continued the conquest of Persia, eventually leading to the fall of the Sasanian Empire in 651. Abu Bakr, a close companion of Muhammad from the Banu Taym clan, was elected the first Rashidun leader and began the conquest of the Arabian Peninsula. The caliphate arose out of the death of Muhammad in 632 CE and the subsequent debate over the succession to his leadership.
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The four Rashidun caliphs were chosen by a small electoral body consisting of prominent members of the Quraysh tribal confederation called shūrā ( Arabic: شُـوْرَى, lit. By the 650s, in addition to the Arabian Peninsula, the caliphate had subjugated the Levant to the Transcaucasus in the north North Africa from Egypt to present-day Tunisia in the west and the Iranian Plateau to parts of Central Asia and South Asia in the east. The Rashidun Army numbered more than 100,000 men at its peak. The Rashidun Caliphate is characterized by a twenty-five-year period of rapid military expansion followed by a five-year period of internal strife. This term is not used in Shia Islam, as Shia Muslims do not consider the rule of the first three caliphs legitimate. These caliphs are collectively known in Sunni Islam as the Rashidun, or "Rightly Guided" caliphs ( اَلْخُلَفَاءُ ٱلرَّاشِدُونَ, al-Khulafāʾ ar-Rāšidūn). It was ruled by the first four successive caliphs (successors) of Muhammad after his death in 632 CE ( AH 11). The Rashidun Caliphate ( Arabic: اَلْخِلَافَةُ ٱلرَّاشِدَةُ, romanized: al-Khilāfah ar-Rāšidah) was the first of the four major caliphates established after the death of the Islamic prophet Muhammad.
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