Soon after Islam was established in the seventh century, a Muslim Empire known as the Rashidun Caliphate rapidly expanded across the Middle East. Yet after only a brief period of stability, the Caliphate collapsed into a civil war over the issue of succession. Some argued that only Muhammad's descendants could rule the Muslim Empire while others felt differently, a division that today has developed into the Muslim world's Sunni-Shiite split.

The Prophet Muhammad

The Prophet Muhammad, a merchant from the city of Mecca in modern-day Saudi Arabia, founded Islam after he heard the word of God revealed to him by the angel Gabriel as he was meditating in a cave. While his new religion was originally met with hostility by the tribes of Mecca, by A.D. 630, Muhammad and his followers had established Islam in the city and founded what would become the first Muslim Empire.

The Rashidun Caliphate

When Muhammad died in 632, the Arabian Peninsula had been largely unified under Islam. His long-time companion and father-in-law Abu Bakr was elected as caliph, or spiritual ruler of the Muslims, and successor to the Prophet. His succession initiated a period known as the Rashidun ("Rightly-Guided" in Arabic) Caliphate. Under Abu Bakr and his successors, Caliph Umar and Caliph Uthman, the Muslim Empire rapidly expanded into Egypt, Persia and the Eastern Mediterranean. Nevertheless, the Rashidun Caliphate and its unified Muslim Empire would be short-lived.

Ali and Muawiyah

In 656, Caliph Uthman was assassinated by rebels. A faction of the Muslim Empire, which had disputed Uthman's succession 12 years earlier, successfully installed Ali, Muhammad's cousin and son-in-law, as the fourth caliph. They declared Uthman's succession invalid as Uthman, unlike Ali, was not directly related to Muhammad. To avenge Uthman's death, his kinsman Muawiyah, then governor of the empire's Syrian province, launched a rebellion against Ali, leading to the first Muslim civil war. Five years into the war, Ali was killed by rebels and Muawiyah declared himself caliph.

Sunni and Shiite

Muawiyah's victory established the Umayyad Caliphate, which over the next hundred years would grow into an immensely wealthy and powerful empire. Yet the war between him and Ali had irrevocably split the Muslim world. Those who accepted Muawiyah as a legitimate caliph became Sunnis, whereas the substantial minority who sided with Ali became Shiites. This Sunni-Shiite divide has caused numerous civil wars across the Muslim world, whether in Iraq, Lebanon, or Syria, and continues to claim lives today. Thus though the split of the Muslim Empire occurred over just one disputed succession many years ago, its reverberations are felt even today.