Brief History Lesson on the Sunni-Shi'ite Schism by Prof. Spic
>Muhammed designates Ali ibn abu Talib, his first cousin / son in law married to his only daughter Fatima, as his successor at the event of Ghadir Khumm (basically he took a huge crowd of people into the scorching hot remote desert in an emergency meeting to tell them that Ali is the #2 guy)
>Muhammed dies 6 months later
>the companions, led by Abu Bakr and Umar, do a coup where they hold an election, voting for Abu Bakr as the first Caliph. Ali does not regard the process as legitimate and does not participate
>Abu Bakr denies Fatima the estate Muhammed gave to her as an inheiritance, and later burns Fatima's house down, killing her
>Abu Bakr dies and is succeeded by Umar, who appoints Mu'awiya as governor of Syria
>Umar dies and is succeeded by Uthman, a wealthy old man
>Uthman gets assassinated by a group of assassins that emerged from a crowd of Ali's supporters, Ali finally becomes Caliph
>Mu'awiya refuses to give the oath of allegiance to Ali unless he mass-imprisons his own supporters, which he isn't going to do
>Ali and Mu'awiya's armies fight a battle, which ends with stalemate
>Ali agrees to negotiate with Mu'awiya
>radical former supporters of Ali (Khawarij) assassinate Ali because they believed by negotiating he committed a sin and lost the right to rule
I kinda forget the details after this point but I think it was basically
>Mu'awiya designates his son Yazid as his own successor
>Mu'awiya or Yazid or the Khawarij has Ali's eldest son Hasan assassinated
>Yazid sends an army to kill Ali's other son Hussein in Karbala, Iraq
>Ali's daughter Zaynab goes to Damascus before Yazid and bitches about him killing her whole family
>Yazid becomes Caliph, ending the Rashidun Caliphate which had oligarchic elections and beginning the Umayyad Caliphate which was hereditary
so basically Sunnis killed Muhammed's family to take over the Caliphate for themselves. Shi'ites believe it was supposed to be Muhammed's family that ruled it, which makes sense. Islam was all about Muhammed's own self-interest, like they're supposed to think of his wives as their mothers, so it would follow that he wanted his son-in-law to succeed him. also the Banu Umaya clan that Mu'awiya was from which ran the trade route from Mecca to Damascus was the 2nd most powerful and rival clan to Muhammed's clan Banu Hashim that ran the Kaaba idol worship business which Mecca was built around. hmmmmmm