Politics, power, anger at feeling oppressed, revolution. Same ol’ reasons for every war.
Focusing on religion sidesteps all of that. Keeps us from seeing how the west wants to divvy up Syria’s natural and architectural resources, and ISIS is a group of really pissed of ppl who are blaming the West for pulling Saddam out of power (they didn’t like Saddam either) and then leaving them to rot.
Besides, ISIS doesn’t do the extensive religious training that the older groups were known for. Religion doesn’t really even play into it anymore. Maybe at one time (even that’s historically debatable) but not now. They’re as Muslim as Westboro Baptist church are Christian.