There are always conspiracy theories for every true one (and the true isn't necessarily the first one either). This is just an international-scale, millennia-spread version of this.

I'm not Christian, just arguing for them using the one thing they lack; logic.

Man-made. The first people like Neanderthals and such unnamed cavemen would have been very uneducated before they could form a society their 2 or 3 member family would be their only form of civilization they wouldn't have been able to understand such things between them as we understand today from the explanations of Scientist like thunder and lightning, earthquakes, hurricanes or natural human things like birth and death. So they imagined these things would occur because of a unseen spirit or a God. They scratched the stories on the cave walls of what they think was happening, people started to believe and spread the word, as time went on the stories continue and changed here and there, it gets written in a book- they read, they believe, they follow- religion formed. Look at the religious mess we're in now. F*cking Neanderthals.

It's the devil that is leading those people to those "religions" and just filling their minds with lies. There is only one real religion!