I'm one of those Ancient Aliens nutters. I mean, full out - I think modern humans are the result of complex genetic engineering on the part of a highly advanced alien civilization that came to Earth looking for resources.
I agree. We have so much evidence pointing to ET's as well as many mysteries that just don't add up here on this planet. There definitely are intelligent beings checking us out, all with different motives. (This gives me an idea for another thread).
I could go into really, really deep detail about it, but the gist of the story is that on Nibiru (the Annunaki's home planet) there were succession wars over their throne, which eventually led to one brother trying to off the other.
They say all legends come from somewhere.
My favourite theory about the Giza Pyramids is that they were built by these gods as basically a fancy landing pad that goes across the Sinai peninsula. There are structures around the world, which mimic exactly the positioning of these pyramids, and found in regions where these cultures wouldn't have the ability to interact with each other.
There is even a pyramid in a lake in Wisconsin. How did all of these civilizations build all of these pyramids around the same time unless they communicated with eachother or had outside help?