Probably the god(s) physically revealing themselves or showing undeniable proof of their power. It'd have to be something that can't be rationalized or explained in any known way, something that shows supernatural divinity, but I'm not sure what exactly it could be. Though keep in mind, if that happened then yes I would accept such an existence just fine.
Then it wouldn't be a matter of believing, it'd just be an established fact. But I still wouldn't worship them or commit myself to any religion, there's no reason to do that and I have no interest.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.