You're making assumptions. Are you sure that no one knew about the 'New World'?
I could point you to a dozen sites that indicate the Egyptians, the Celtics, etc knew very well what was here before our 'forefathers' ever arrived.
You might want to read up on the possibility that the Aztec were in Utah before heading into Mexico.
There are thousands and thousands of pyramids worldwide. Where were the first pyramids?
Were they responsible for the mystery religion or did some other group corrupt their society with it? Were the true Egyptians already gone and the Babylonians just took over their sites?
So many questions and no answers.