Ok, I think hadiths play a role in the conflict too because they reject each others hadiths. They basically arguing over one matter but each using a different set of books with different narratives lol Cant see them reaching a conclusion with that any time soon! Shias dont like Aisha the child bride.
Sikhs are really lucky that we dont have major differences in Sikh sects like muslims and Christian's do. The worst I can think of is the nirankaris and their on going line of gurus but they are pretty much are out of the fold of Sikhi now and did whatever damage they wanted to back in the 80s.
That's not entirely true.
There is a Hadith (and I'm paraphrasing here as I don't remember all the details) when the prophet initially invited all the quresh tribes to dinner to invite them to Islam. He asked the question, who will be my brother (in faith), my friend and my successor (khalifa). Imam Ali immediately stood up. The prophet asked him to sit down (as he was still quite young, though extremely loyal to the prophet from day one). The prophet asked the question again, and again the same thing happened. On the third time, when Imam Ali stood up, the prophet said, very well, you will be my brother, my friend and my successor. This hadith is found in both sunni and shia books.
There is also a verse in the quran (and please correct me if I'm wrong) where Allah says that he chooses his khalifa. Depending on the context of this verse, this could invalidate the khalifate of Abu Bakar and validate the divinity of Ali being the khalifa.
There is also a "Hadith-e-Noor" (found in both sunni and shia books) in which the prophet says, Me and Ali are created from the same light.
These (and many others) are just some of the points which could point to the divine claim that Imam Ali was indeed the divine successor to the prophet.
But yes, there was plenty of killing of the family of the prophet. And many battles ensued, which resulted in parts of the quran being lost. But...that's a different topic entirely....