God... Truth or fiction?

I agree that in many cases, the "elite" were interested in Christianity, but more as a political tool. However, I don't think that the people, anywhere, would ever voluntarily change their faith:
Just imagine a situation where a state-sponsored revival of paganism begins in Russia right now. I think everything is clear:

Regarding Islam. Things are even more complicated here. A prophet, known for his far from pious life and having a harem, is not particularly interesting to those in power, as you can't make an idol out of him, and certainly not to the people. Only by force!:)