Excerpts from Books and Wikipedia
"Muawiya, governor of Syria, rebelled against Caliph Ali in 657, after he failed to punish the murderers of his cousin Caliph Uthman (644-656). . . . In 660, Muawiya proclaimed himself caliph in Jerusalem in a bid to drive Ali from power. However, he was not complicit in Ali's murder in January 661. Ali's supporters, known as Shi'ites, transferred their allegiance to his son Hasan but he resigned his claim to the caliphate. Within seven months of Ali's death, Muawiya had won control of the caliphate supported by his Sunni followers. . . . Muawiya's original power base had been in Syria, so he moved his capital from Medina to Damascus, which had better communications with the rest of the caliphate." [1001 Days]