Edgar Cayce, America’s sleeping prophet, said that Atlantis was an advanced alien civilization that destroyed itself by global warming and causing the sea levels to rise and its own demise and is somehow linked to North America.
He died in 1945, pre Roswell.
In 1968, Chariots of the Gods? by Erich von Däniken took you on a world journey with pictures making all kinds of archeological connections to attempt to show that MAYBE aliens did all of those things.
So, they got the ball rolling with this stuff. My grandmother was into this stuff when I was a kid and so I learned all about it then. I dismissed it somewhere in my mid-teens as modern mythology (as I’d discovered Joseph Campbell (and Jung by proxy)), useful for a people lacking this kind of thing in their lives and mostly harmless.