The early Caliphs
After Mohammed died (632), an assembly of Moslems in Mecca elected Abu Bakr, Mohammed's closest adviser, as the first 'khalifat rasul Allah' (successor of the Prophet of God), or caliph.
The second caliph, Omar, directed the conquest of Egypt, Syria and Mesopotamia.
The third and last of the elected caliphs, Othman, laid the foundation for the hereditary Caliphate of the Omayyad family. Othman favoured the Omayyads and was murdered by opponents.
Ali ibn Abi Talib, cousin of Mohammed, was an early convert to Islam. A dispute over his rights to succeed Mohammed forced him into retirement. But when the third caliph - Othman - was murdered, Ali was invited by the Moslems of Mecca to accept the caliphate. He based his caliphate on ideals of social justice and equality. This led to a rebellion by the aristocracy of Mecca.
The governor of Damascus, Mo'awiya, a kinsman of Othman's family, wanted to avenge the death of his cousin Othman. He challenged his rival Ali for the Caliphate in an Arab civil war and defeated him.
The last chance to avert a split between the Shi'ah (followers of Ali) and the Omyyads was lost when Ali's son Husayn was ambushed and killed at Karbala in Iraq in 680.