Islam is complicated. They each believe in succession but how they go about it so different.
Sunni’s have the Caliphs, which are political/military leaders and their authority is decentralized in theory. Succession comes up to a consensus vote between a group of spiritual leaders.
Sounds good. But too often the reality was either inheritance or military force.
Shia’s have the line of Imams stemming back to Muhammad through the bloodline.
The Shiites is basically “Iran” yet because they’re so structured, they are more powerful in certain ways the Sunni’s can never match.
The Sunnis influence is far broader and diluted, because national influence often overtakes religious influence.
Since Sunnis make up like 90% of Muslims worldwide, statistically more likley the radicalized groups would come from them. But they’re also more prone because it’s easier for a group of people to decide they want to restore the Caliphate to some imaginary glorious past with them on top. And so, it begins.