Islam's Expansion in the 7th Century

At the beginning of the seventh century, Islam was a religion practiced by a small band of persecuted believers in Mecca. By the end of the seventh century, the religion's name was attached to an empire that ranged from the Atlantic Ocean to India. The seventh century saw 10 Muslim rulers: one prophet, four "rightly guided caliphs" and five caliphs from the Umayyad dynasty.

Muhammad began receiving revelations in the year 610, and the first believer was his wife, Khadija. Through time Muhammad began attracting more followers as well as fierce persecution in his hometown of Mecca. Some Muslims migrated to Abyssinia -- modern-day Ethiopia -- to escape persecution, and eventually things became so dangerous Muhammad himself had to flee Mecca. The Muslims fled 200 miles north to Medina.

The Hijra, the moving of Muhammad's community to Medina, begins the Muslim calendar, and it marks the first time a Muslim was a head of state. The community lived by Muslim principles alongside its Jewish neighbors, and Surah 3, verse 110 of the Quran calls this community the greatest in history. In 630 the Muslims conquered Mecca, and by Muhammad's death in 632 Islam ruled over most of the Arabian Peninsula.

Under the four "rightly-guided caliphs" -- Abu Bakr, Umar, Uthman and Ali -- the Islamic Empire spread north into former Byzantine territory, conquering the Christian Holy Land. During this period the empire also spread west into Egypt and east into the Persia, defeating the rapidly crumbling Sassanid Dynasty. Many of these areas were Christian, leading to agreements such as the pact of Umar, in which Christians agreed to not build new churches, convert Muslims and act in a generally submissive manner in exchange for Muslim protection.

After Ali, the Umayyad caliphate took power under Mu'awiyah followed by his son, Yazid. The Umayyad Dynasty lasted from 661 until 750 and oversaw several civil wars as well as further expansion of Muslim territory. The Umayyads expanded the empire west across northern Africa all the way to the Atlantic Ocean, north into Spain and east as far as modern-day Afghanistan. The Umayyads also expanded further north into Byzantine territory.

There are several explanations given for the Islamic Empire's rapid success ranging from Divine Will to dumb luck to the power of religious fervor, but scholars generally point to a diverse range of causes. One major cause was the constant warfare between the Byznantines and the Sassanids that weakened both empires considerably.