The idea there’s some barrier to entry to America

That no one could surmount til the 15th century,

Is absolutely absurd.

Why does anyone believe this?

Especially with the mountain of evidence disproving it!

In fact, I think the whole thing was made up around 300 years ago.

Right around that 1776 area. Lots of things changed about the world around 300 years ago. If you study history you’ll start to notice the patterns.