Succession to Muhammad in the context of "Middle Ages"

Sunni Islam is the largest branch of Islam and the largest religious denomination in the world. It holds that Muhammad did not appoint any successor and that his closest companion Abu Bakr (r. 632–634) rightfully succeeded him as the caliph of the Muslim community, being appointed at the meeting of Saqifa. This contrasts with the Shia view, which holds that Muhammad appointed Ali ibn Abi Talib (r. 656–661) as his successor. Nevertheless, Sunnis revere Ali, along with Abu Bakr, Umar (r. 634–644) and Uthman (r. 644–656) as 'rightly-guided caliphs'.

The term Sunni means those who observe the sunna, the practices of Muhammad. The Quran, together with hadith (especially the Six Books) and ijma (scholarly consensus), form the basis of all traditional jurisprudence within Sunni Islam. Sharia legal rulings are derived from these basic sources, in conjunction with consideration of public welfare and juristic discretion, using the principles of jurisprudence developed by the four legal schools: Hanafi, Hanbali, Maliki and Shafi'i.

The history of Islam is believed, by most historians, to have originated with Muhammad's mission in Mecca and Medina at the start of the 7th century CE, although Muslims regard this time as a return to the original faith passed down by the Abrahamic prophets, such as Adam, Noah, Abraham, Moses, David, Solomon, and Jesus, with the submission (Islām) to the will of God. According to the traditional account, the Islamic prophet Muhammad began receiving what Muslims consider to be divine revelations in 610 CE, calling for submission to the one God, preparation for the imminent Last Judgement, and charity for the poor and needy. As Muhammad's message began to attract followers (the ṣaḥāba) he also met with increasing hostility and persecution from Meccan elites. In 622 CE Muhammad migrated to the city of Yathrib (now known as Medina), where he began to unify the tribes of Arabia under Islam, returning to Mecca to take control in 630 and order the destruction of all pagan idols. By the time Muhammad died c. 11 AH (632 CE), almost all the tribes of the Arabian Peninsula had converted to Islam, but disagreement broke out over who would succeed him as leader of the Muslim community during the Rashidun Caliphate.

The early Muslim conquests were responsible for the spread of Islam. By the 8th century CE, the Umayyad Caliphate extended from al-Andalus in the west to the Indus River in the east. Polities such as those ruled by the Umayyad and Abbasid caliphates (in the Middle East and later in Spain and Southern Italy), the Fatimids, Seljuks, Ayyubids, and Mamluks were among the most influential powers in the world. Highly Persianized empires built by the Samanids, Ghaznavids, and Ghurids significantly contributed to technological and administrative developments. The Islamic Golden Age gave rise to many centers of culture and science and produced notable polymaths, astronomers, mathematicians, physicians, and philosophers during the Middle Ages. By the early 13th century, the Delhi Sultanate conquered the northern Indian subcontinent, while Turkic dynasties like the Sultanate of Rum and Artuqids conquered much of Anatolia from the Byzantine Empire throughout the 11th and 12th centuries. In the 13th and 14th centuries, destructive Mongol invasions, along with the loss of population due to the Black Death, greatly weakened the traditional centers of the Muslim world, stretching from Persia to Egypt, but saw the emergence of the Timurid Renaissance and major economic powers such as the Mali Empire in West Africa and the Bengal Sultanate in South Asia. Following the deportation and enslavement of the Muslim Moors from the Emirate of Sicily and elsewhere in southern Italy, the Islamic Iberia was gradually conquered by Christian forces during the Reconquista. Nonetheless, in the early modern period, the gunpowder empires—the Ottomans, Timurids, Mughals, and Safavids—emerged as world powers.

Shia Islam is the second-largest branch of Islam. It holds that Muhammad designated Ali ibn Abi Talib (r. 656–661) as both his political successor (caliph) and as the spiritual leader of the Muslim community (imam). However, his right is understood to have been usurped by a number of Muhammad's companions at the meeting of Saqifa, during which they appointed Abu Bakr (r. 632–634) as caliph instead. As such, Sunni Muslims believe Abu Bakr, Umar (r. 634–644), Uthman (r. 644–656) and Ali to be 'rightly-guided caliphs', whereas Shia Muslims regard only Ali as the legitimate successor.

Shia Muslims believe that the imamate continued through Ali's sons, Hasan and Husayn, after which various Shia branches developed and recognized different imams. They revere the ahl al-bayt, the family of Muhammad, maintaining that they possess divine knowledge. Shia holy sites include the shrine of Ali in Najaf, the shrine of Husayn in Karbala, and other mausoleums of the ahl al-bayt. Later events, such as Husayn's martyrdom in the Battle of Karbala (680 CE), further influenced the development of Shia Islam, contributing to the formation of a distinct religious sect with its own rituals and shared collective memory.