What was the difference between the Shea and the Sunni?

The Sunni and the Shia are two major denominations in Islam that differ primarily in their beliefs about the rightful succession of leadership after the death of the Prophet Muhammad. Sunnis believe that leadership should be elected, while Shias believe that leadership should be passed down through the Prophet's bloodline. This historical disagreement has led to other theological and jurisprudential differences between the two groups.