Muhammad, born in the Arabian peninsula, experienced a religious vision, after which he preached to the people to give up their idols and submit to the one indivisible God. He believed in the same God as the Christians and Jews and taught strict monotheism. Islam, the religion based on Muhammad’s teachings, appropriated much of the Old and New Testaments of the Bible. After Muhammad’s death, his followers gathered his revelations, eventually producing the Qur’an.

Within the span of a century, Muslims carried their faith from the Arabian peninsula through the Middle East, to North Africa and Spain, and to the borders of China and India. Successors to Muhammad established the caliphate, which through two successive dynasties coordinated rule over Muslim lands. A key challenge faced by the caliphate was a fundamental division in Muslim theology between the Sunnis and the Shi’a.

Over time, many parts of the Muslim empire gained considerable local independence. Far-flung territories such as Spain began to break away from the Baghdad-centered caliphate. By the tenth century Turks played a more important role in the armies and came to be the effective rulers in much of the Middle East. They were succeeded by the Mongols, who invaded the Middle East in the thirteenth century and ruled the central Muslim lands for eighty years.

Muslim society was distinctly hierarchical. In addition to a structure that privileged the ruling Arab Muslims over converts to Islam, then over Jews, Christians, and Zoroastrians, there were also a substantial number of slaves, generally war captives. Slaves normally were converted to Islam and might come to hold important positions, especially in the army. Distinctions between men and women in Islamic society were strict. Over time, the seclusion and veiling of women became common practices, especially among the well-to-do.

Islam did not discourage trade and profitmaking. By land and sea Muslim merchants transported a rich variety of goods across Asia, the Middle East, Africa, and western Europe. As trade thrived, innovations such as money orders to bankers, bills of exchange, and joint stock companies aided the conduct of business.

Wealth from trade made possible a gracious and sophisticated culture in the cities of the Muslim world, especially Baghdad and Córdoba. During this period Muslim scholars produced important work in many disciplines, especially mathematics, medicine, and philosophy. A new spiritual and intellectual tradition arose in the mystical practices of Sufism. Muslims, Christians, and Jews interacted in many ways during this period. At the time of the Crusades and of the Christian reconquest of Muslim Spain, polemical anti-Christian writings appeared, but in other periods Muslim views were more positive. Many Christians converted in the early centuries of the spread of Islam. Others such as the Mozarabs assimilated into Muslim culture while retaining their religion.