Different denominations of the same religion can't get along with each other. Therefore, religion doesn't unify, it divides.
We can see this divide in the Holocaust, in which Nazis gave up their Christian faiths to follow the new beliefs of Nazism. While Jews were being starved, beaten, tossed into ovens, and made into lamp shades, many in Germany ignored their suffering and supported the mad man in charge.
If, on the other hand, everyone stuck to the Christian religion, they wouldn't have tolerated such behavior. So, in some sense, I see what you mean about religion unifying.
I see we have the power to change our attitudes, learn from our mistakes.
Regards Tony