Rashidun in the context of "Rashidun Caliphate"

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 spread of Islam spans almost 1,400 years. The early Muslim conquests that occurred following the death of Muhammad in 632 CE led to the creation of the caliphates, expanding over a vast geographical area; conversion to Islam was boosted by Arab Muslim forces expanding over vast territories and building imperial structures over time. Most of the significant expansion occurred during the reign of the rāshidūn ("rightly-guided") caliphs from 632 to 661 CE, which were the first four successors of Muhammad. These early caliphates, coupled with Muslim economics and trading, the Islamic Golden Age, and the age of the Islamic gunpowder empires, resulted in Islam's spread outwards from Mecca towards the Indian, Atlantic, and Pacific Oceans and the creation of the Muslim world. The Islamic conquests, which culminated in the Arab empire being established across three continents (Asia, Africa, and Europe), enriched the Muslim world, achieving the economic preconditions for the emergence of this institution owing to the emphasis attached to Islamic teachings. Trade played an important role in the spread of Islam in some parts of the world, such as Indonesia. During the early centuries of Islamic rule, conversions in the Middle East were mainly individual or small-scale. While mass conversions were favored for spreading Islam beyond Muslim lands, policies within Muslim territories typically aimed for individual conversions to weaken non-Muslim communities. However, there were exceptions, like the forced mass conversion of the Samaritans.

Muslim dynasties were soon established and subsequent empires such as those of the Umayyads, Abbasids, Mamluks, Seljukids, and the Ayyubids were among some of the largest and most powerful in the world. The Ajuran and Adal Sultanates, and the wealthy Mali Empire, in North Africa, the Delhi, Deccan, and Bengal Sultanates, and Mughal and Durrani Empires, and Kingdom of Mysore and Nizam of Hyderabad in the Indian subcontinent, the Ghaznavids, Ghurids, Samanids in Persia, Timurids, and the Ottoman Empire in Anatolia significantly changed the course of history. The people of the Islamic world created numerous sophisticated centers of culture and science with far-reaching mercantile networks, travelers, scientists, hunters, mathematicians, physicians, and philosophers, all contributing to the Islamic Golden Age. The Timurid Renaissance and the Islamic expansion in South and East Asia fostered cosmopolitan and eclectic Muslim cultures in the Indian subcontinent, Malaysia, Indonesia and China. The Ottoman Empire, which controlled much of the Middle East and North Africa in the early modern period, also did not officially endorse mass conversions, but evidence suggests they occurred, particularly in the Balkans, often to evade the jizya tax. Similarly, Christian sources mention requests for mass conversions to Islam, such as in Cyprus, where Ottoman authorities refused, fearing economic repercussions.

The Muslim conquest of the Levant (Arabic: فَتْحُ الشَّام, romanized: Fatḥ al-šām; lit. 'Conquest of Syria'), or Arab conquest of Syria, was a 634–638 CE conquest of Byzantine Syria by the Rashidun Caliphate.

A part of the wider Arab–Byzantine wars, the Levant was brought under Arab Muslim rule and developed into the provincial region of Bilad al-Sham. Clashes between the Arabs and Byzantines on the southern Levantine borders of the Byzantine Empire had occurred during the lifetime of Muhammad, with the Battle of Muʿtah in 629 CE. However, the actual conquest did not begin until 634, two years after Muhammad's death. It was led by the first two Rashidun caliphs who succeeded Muhammad: Abu Bakr and Umar ibn al-Khattab. During this time, Khalid ibn al-Walid was the most important leader of the Rashidun army.

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.

The Shafi'i school or Shafi'i Madhhab (Arabic: ٱلْمَذْهَب ٱلشَّافِعِيّ, romanized: al-madhhab al-shāfiʿī) or Shafi'i is one of the four major schools of Islamic jurisprudence, belonging to the Ahl al-Hadith tradition within Sunni Islam. It was founded by the Muslim scholar, jurist, and traditionist al-Shafi'i (c. 767–820 CE), "the father of Muslim jurisprudence", in the early 9th century.

The other three schools of Sunnī jurisprudence are Ḥanafī, Mālikī and Ḥanbalī. Like the other schools of fiqh, Shafiʽi recognize the First Four Caliphs as the Islamic prophet Muhammad's rightful successors and relies on the Qurʾān and the "sound" books of Ḥadīths as primary sources of law. The Shafi'i school affirms the authority of both divine law-giving (the Qurʾān and the Sunnah) and human speculation regarding the Law. Where passages of Qurʾān and/or the Ḥadīths are ambiguous, the school seeks guidance of Qiyās (analogical reasoning). The Ijmā' (consensus of scholars or of the community) was "accepted but not stressed". The school rejected the dependence on local traditions as the source of legal precedent and rebuffed the Ahl al-Ra'y (personal opinion) and the Istiḥsān (juristic discretion).