I would actually take that earlier statement, "religion causes more wars and problems than anything else" and make it "differences cause more wars and problems than anything else."
I mean, communism isn't a religion and America fought a lot of wars simply because other countries had a communist government.
Even further back, we fought the revolutionary war and the civil war, wars fought for freedom, rights, and moral obligation to withhold those rights.
I'm not saying no war has ever been started because of religion, far from it. I'm merely saying that wars and problems are caused because of many many things, you can't just pick one of the reasons specifically and say "this is the root of all evil." If you're going to decide on a common reason as to the worlds problems, it should be vague enough to cover a wide array of causes.