وَمَا وَقَعَ مِنَ الِاخْتِلَافِ بَيْنَ الشِّيعَةِ وَأَهْلِ السُّنَّةِ
And the disagreement that occurred between Shia and Sunnis.
The civil conflicts are linked to a distinct theological controversy about how the imamate was determined. The question is whether leadership after the Prophet ﷺ was fixed by explicit designation of a person or established through allegiance, consultation, and other evidence.
This cannot be reduced to the history of one battle. It concerns the principles of designation, textual indication, communal consultation, and the establishment of a caliphate.