Hi I'm sunni and I don't understand the differences between shias and sunnis and why it's such a big deal? Like I've tried researching but it all goes back to like Abu Bakr and those people and I don't understand
The basic difference is not having the dilemma of praising killers and usurpers in the same breath as the Prophet (saw) and his Pure Progeny (as).
1) Prophet Muhammad (saw) appointed his successor at Ghadir Khumm: his cousin and son-in-law, Imam Ali Ibn Abi Talib (as). Therefore, Abu Bakr’s claim to Caliphate was an infringement on the rights of Imam Ali (as).
2) While Imam Ali (as) and other companions were busy attending to the Prophet’s washing and burial, Abu Bakr and Umar went to Saqifa to seize the Caliphate. This is the meeting where the future of the Ummah was decided, and it took place without the attendance of Imam Ali (as), nor was his opinion sought. Imam Ali (as) did not recognize Abu Bakr’s claim.
3) Abu Bakr took Fadak away from Sayeda Fatima (sa), which was the Prophet’s gift to his daughter. She remained disgruntled with him until she died.
4) Abu Bakr launched a War of Apostasy (Ridda Wars) upon the people who withdrew their Zakat. Many of those killed were simply Muslims who did not recognize Abu Bakr’s Caliphate and therefore did not pay him their Zakat. The war was launched immediately after Abu Bakr’s inauguration; while Zakat can be paid anytime during the year. He was ignorant and unjust. He refused to punish the rapist/murderer Khalid Ibn Waleed (Allah’s Curse be upon him).
5) Abu Bakrs actions as Caliph were unacceptable. He had taken the rights and property away from the Ahlulbayt (as), and killed people unjustly.