What disagreement led to the division of Sunni and Shia Muslim?

What are the differences between Sunnis and Shiites? Their beliefs over who should have succeeded the Prophet Muhammad is the key theological difference between the two. Sunnis also have a less elaborate religious hierarchy than Shiites have, and the two sects' interpretation of Islam's schools of law is different.

Explanation:

why was the national assembly formed by the third estate?

the estates-general had not been assembled since 1614, and its deputies drew up long lists of grievances and called for sweeping political and social reforms. the third estate, which had the most representatives, declared itself the national assembly and took an oath to force a new constitution on the king.

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