Excerpts from Books and Wikipedia
"Ultimately Ali decided to accept the title of caliph. Later, he wrote to the Muslim governor of Egypt about his decision: “It could not even be imagined that the Arabs would snatch the seat of the caliphate from the family and descendents of the Holy Prophet, and that they would be swearing the oath of allegiance for the caliphate to a different person. At every stage I kept myself aloof from that struggle of supremacy and power-politics till I found the heretics had openly taken to heresy and schism and were trying to undermine and ruin the religion preached by our Holy Prophet.” He believed that establishing the caliphate in the Banu Umayya clan would make it unambiguously into a political position, destroying its close connection to Muhammad and his mission.16 Yet to prevent this from happening, he would be forced to fight. Aishah and her supporters had already left Medina, heading for the city of Basra at the head of the Persian Gulf, where they hoped to gather more supporters for their cause. Ali gathered soldiers and followed them. In December of 656, six months after he had accepted the title, he met his enemies outside Basra’s walls in the Battle of the Camel." [Wikipedia]