I’ve been reading some articles lately that suggest that Native Americans actually had a thriving civilization here, but a plague wiped out possibly as many as 90% of them, which is why the Vikings had quite a challenge with them but subsequent visitors did not. It may be that they caught something from the vikings.
There are stories of settlers coming across spectacular gardens, roads, etc. And there are a lot of odd and large mounds (hundreds of feet in diameter and many tens of feet in hight) here and there that nobody has bothered to check out for some reason.
This story is a perfect example. The Spanish made contact with this city and retreated but they left behind smallpox, and other diseases that wiped the area out making it a piece of cake for later Europeans to move in. Some say pigs were a major disease vector. The Spanish would leave pigs behind in an initial exploration as a future food source. The pigs multipley and expand cleaning out areas that never saw a European.
I follow this guy on youtube and he discusses the mound builders quite a bit.
https://www.youtube.com/watch?v=1MM8UqbWP30
I believe that there are theories that both Americas were as densely populated as Europe several times, but that hemorrhagic fevers swept through both continents several times.
The lack of varied livestock (particularly cattle) meant that their immune systems weren’t subject to as constant a pressure pressure, and their populations didn’t maintain as rubust an immune system as populations in Africa, Asia, and Europe.
I put more stock in the idea that the little ice age played a big role. Wars too.
And there are a lot of odd and large mounds (hundreds of feet in diameter and many tens of feet in hight) here and there that nobody has bothered to check out for some reason.
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Mostly these structures were destroyed to make way for farms, highways and so forth.
The reason they are neglected is that the findings would very likely contract the current meme used by ‘native’ tribes to legally justify their Federal hand outs and Special legal status (they have Rights guaranteed by the Constitution, all others have mere privileges which can be revoked at any given time) namely: they were created here; there was no one here before them. Therefore, any findings are theirs to claim and dispose of; no studying of them allowed. No archeologists wants to go through the pain and high expenses of court battles they cannot win.