I'd doubt whether religious belief as such is what motivates even Al Qaeda, as against resentment about essentially political issues.

The point is, even in a world where religious difference were absent, the same kinds of conflicts we see would still arise. The slogans and the rationale would be different.

In a way it's akin to the situation with the Cold War. The antagonism between Russia and the US and others was assumed to be about ideology - if the Russians stopped believing in "Communism" we'd all be friends. It hasn't worked out that way. It was always more about power and stuff like that.