The Ridda Wars of 632 through 633 A.D. were a series of campaigns during which the first elected Islamic Caliph, Abu Bakr, defeated rebellious Arab tribes just after Mohammed's death. "Ridda" translates roughly to "apostasy."
The large Islamic empire Mohammed had built began to break apart when he died. Several groups rose up to back self-declared caliphs, or leaders of the Islamic faith. In a series of campaigns, Abu Bakr sent his general Usama ibn Zaid to recapture the rebels either through defeating them in battle or by negotiating with them. In the 27 months of his rule before he died of fever, Abu Bakr had reconquered Arabia and Persia and added Syria to the Caliphate.
The echoes of the Ridda Wars continue in modern times in the strife between Sunni and Shi'a Muslims. The Shi'a are the ideological descendants of the rebels.