The difficulty with this question is determining when a war between two states is primarily caused by religion and when a war between two states is primarily caused by some other reason (a disputed succession, mutual desire for a limited resource or area of territory, etc.) and religion simply happens to be part of the mix. If two foreign nations each support a claimant to the throne in a third nation, and these two claimants are of differing religions, is the resulting war caused more by religion or by politics? Or both, or neither? It's a difficult question in all but the most clear-cut cases.

As you say, the idea that religion causes every single war is not true. In fact, though it is somewhat unacademic of me, I advise you to call the next person who suggests such a thing an idiot, and dare them to come up with a justification for calling the Vietnam War or World War 2 religious wars.