In the century after Muhammad's death in 632, Arab armies built one of the largest empires the world had yet seen, stretching from Spain to Central Asia. These conquests were directed by the Damascus-based Umayyad dynasty — but rapid expansion created deep tension. Non-Arab converts to Islam, especially Persians (the mawali), were treated as second-class and taxed more heavily.

In 750 this resentment erupted. A movement rising from Khorasan (modern northeastern Iran), gathering under black banners, brought to power the Abbasids — descendants of Muhammad's uncle Abbas. At the Battle of the Zab the last Umayyad caliph was defeated and the dynasty was almost entirely purged. One escaping Umayyad prince fled to Spain and founded a separate state in al-Andalus — the first lasting split in the Islamic world.

The Abbasids moved the capital from Damascus to Baghdad, which they built from scratch in 762. This geographic shift was not symbolic: the caliphate now leaned not on the Mediterranean but on older Persian and Mesopotamian traditions. Persian secretaries, viziers and scholars rose to prominence. This multi-ethnic, cosmopolitan setting made possible, in the following century, the founding of the House of Wisdom in Baghdad, the translation of Greek, Indian and Persian science into Arabic, and the birth of algebra.

The Abbasid Revolution was therefore not merely a change of dynasty but the turning point that set the direction of Islamic civilisation: the threshold between an age of conquest and an age of science and culture.