The issue of leadership following Muhammad’s death caused immediate tensions within the Islamic ummah even as the first four caliphs, the Rashidun, oversaw significant territorial expansion. Tensions between the family of Muhammad—especially his son-in-law Ali, the fourth caliph—and the Umayyads resulted in a civil war that brought Islam’s first dynasty to power

While the Arabs of northern Arabia were uniting as a capable fighting force looking for opportunities to expand, the Byzantines and Sasanian Empires were at a low ebb. In the early seventh century, the Byzantine Empire had won a long and costly war against the Sasanians, sometimes fought on both sides by proxies from northern Arabia, but now the combatants were exhausted and…

caliph — an Islamic title designating a spiritual and secular leader. caliphate — an area under the control of a Muslim ruler called a caliph. Rashidun — a term meaning “rightly guided” that describes the first four caliphs after Muhammad’s death: Abu Bakr, Umar, Uthman, and Ali. ummah — the community of Muslims.