Well, you know, the idea with Satan might work if he and his minions were able to obliterate the vast majority of mankind and decimate our technological capabilities, effectively setting us back in the Stone Age. In that case, we'd probably have to have a renaissance of some sorts, in order to rebuild and combat the forces of evil.

EDIT: If we were going to fight Satan, the idea to base the story on the Book of Revelation as some people have mentioned (i.e. The Four Horsemen) might be a good one.