Final answer:
Sunni and Shi'a Muslims differ mainly in their beliefs about leadership succession after Prophet Muhammad's death, with Sunnis supporting Abu Bakr and Shi'as supporting Ali. They share core religious texts and many practices. Throughout history, their relationship has oscillated between periods of peace and conflict.
Step-by-step explanation:
The split between Sunni Muslims and Shi'a Muslims stems from the debate over succession after the Prophet Muhammad's death. Sunnis, who comprise about 84 to 90% of Muslims today, believed that the leader should be an effective and dynamic leader, which led to Abu Bakr, Muhammad's father-in-law, becoming the first caliph. In contrast, Shi'ites, representing about 10 to 15% of Muslims, believed that the leader should be a member of the Prophet's family, specifically his son-in-law Ali. This caused the two groups to have some theological differences, as well as differences in their structures of leadership, with Sunnis typically electing leaders while Shi'as look to their imams for guidance.
In terms of similarities, both Sunnis and Shi'ites share the same sacred writings, believe in the five pillars of Islam, and practice many of the same traditions. Sometimes, these two major sects have lived in relative peace, but there have been periods of conflict as well, particularly in regions where geopolitical factors emphasize the divide. For instance, the Persian Empire, now Iran, made Shi'ism the state religion in the 16th century, distinguishing it from its Sunni neighbors and laying the groundwork for regional tensions.
Throughout history, the relationship between Sunni and Shi'a Muslims has varied. During the Abbasid period, there was not a complete divide, and Sunnis respected the progeny of Muhammad even if they didn't agree on the exclusive right to leadership from Ali's lineage. However, as the rivalry grew, the distinction between Sunni and Shi'a beliefs solidified into the more defined sects that we see today.