Why did islam split into two similar but opposing groups

Islam split into two similar groups because Shia Islam are the two major denominations of Islam. They chose sides following the death of the Islamic prophet Muhammad in AD 632. A dispute over succession to Islamic prophet Muhammad as a caliph of the Islamic community spread across various parts of the world, which led to the Battle of Jamal and Battle of Siffin.

wait history, who want to talk about history, boring.