to by the Sunni as the Rashidun (rightly-guided) Caliphs, though only Ali is recognized by the Twelver Shia. Later successions Abu Bakr's view that the caliphate should remain within the Quraysh tribe persisted in later generations. According to Cooperson, however, this definition of the caliphate had its costs. First, it facilitated the rise of the Umayyads who, despite being of the Quraysh, were among the most powerful enemies of Muhammad before their late conversion to Islam. Their rise to power marginalized both the Muhajirun and the Ansar, and reduced the caliphate, as an institution, to no more than a worldly kingship. Second, according to Cooperson, was the exclusion of Ali, who, insofar as the kinship of the Quraysh with Muhammad was concerned, had an arguably better claim to the caliphate. Ali eventually became caliph, but not in time to stop the rise of the Umayyads. After the assassination of Ali in 661, his eldest son, Hasan, was elected caliph in Kufa. Muawiya then marched on Kufa with his army, whereas Hasan's military response to Muawiya suffered defections in large numbers, largely facilitated by military commanders and tribal chiefs who had been swayed to Muawiya's side by promises and offers of money. Under attack from Muawiya and after a failed assassination attempt on his life, a wounded Hasan ceded the caliphate to Muawiya in 661. Notably, under their agreement, it is said that Muawiya appointed Hasan as his successor. However, Hasan died in 669 at the age of forty six, before Muawiya. It is believed that he was poisoned at the instigation of Muawiya. Before his death in 680, Muawiya arranged for the succession of his son, Yazid, who is often remembered as a debaucher who openly violated the Islamic norms. In particular, Muawiya summoned a council (shura) of the Muslim elite in 676 and won their support through flattery, bribes, and threats. Notably, Muawiya was unsuccessful in securing the oath of allegiance from Hasan's younger brother, Husayn, who, after Muawiya's death, publicly denounced Yazid's legitimacy. In 680, after surrounding them in Karbala and cutting off their access to water for multiple days, Yazid's forces slaughtered Husayn, alongside his family and his small group of supporters. The women and children were taken prisoner and marched to Kufa and then Damascus, some of whom are said to have perished from mistreatment. The tragic death of Husayn and his supporters marked the Second