Why Does Religion Cause War?

I know, I know. Religion causes war because different religions argue over their validity. Muslims want things to turn out their way, Christians want it theirs, and Buddhists don't care. But this all seems trivial to me. From what I know about religion, these traditions are not the core of religion. they are just part of it. Let me explain.

A few years ago I was reading Freidrich Schleiermacher's On Religion: Speeches to the Cultured Despisers, and I noticed that he drew a line between religion and a religious tradition. Religion is an experience you have when you realize that you did not decide your own existence. Some may argue that their parents decided when they had sex. But who decided the parents' existence? Go all the way down the line to the Big Bang, and ask: who decided the existence of the energy, molecules, etc. that caused the Bang? There is something that has to presuppose the existence of everything. So, religion is when we realize that.

Now a religious tradition is very different. We will call the maker of existence God, for the sake of understanding. What did God get in return for making everything? He got nothing. It seems as though He made everything out of good will. The goal of a religious tradition is to thank God for the totally selfless act of giving us ourselves. Each tradition may choose to thank God in different ways. Why fight over the way to thank God?

Please post comments or disagreements. I would really like to get a better grasp on this.