It wasn’t and isn’t a “stupid dispute”.
It started as a war of succession; who would be the next ruler if a burgeoning Islamic state.
But since then Sunnis has become quite divergent from Shia.
Sunnis are “scripture only” ie they adhere only to the Quran + the Hadiths + the Sirah.
Shia have interpreters of the Scriptures like
1. The largest group, the 12er Shia’s who are in iran have AyatollahS.
2. Syedna Bohris have a Suedna who interpreted that jihad is no longer needed so they are non violent.
3. Ismailis who have the Aga khan, who interpreted the same as the Syedna
Alright, I understand power struggles for control of an empire, and ideological differences over religious interpretations. But one is worldly, and the other is spiritual; they don’t belong together. That they’ve been feuding for 1,400 years over it is stupid and ridiculous. But I suppose that’s what you get when you turn tribal behaviors and lusts for power and domination into a religion. You get a religion that’s a lie.