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.