Monotheism
<Splinx makes a very good point. Polytheism was innocent was Gods would fight each other for power and left humans out of their wars.
Monotheism is a totally different matter: Christianity has a UNIVERSAL VOCATION.
It means God is love, God can only be good to all humans, therefore you must respect and love God. But if you don't, troubles begin. Because it was inconceavable, at the time, not to want to have anything to do with God. And also, because he's so good and powerful, he cannot be criticized, contested. And, being allmighty, he's the only one that can be held responsible for the killings humans did to defend his name.
Really, monotheism is the source of a huge amount of pain and misery.
Raoul