Pure liberal BS - there weren’t no where near 100 million Indians. There is no such thing as Native Americans. I am a native American. I was born in Brooklyn, NYC so that makes me native to this country. Indians came across some land bridge from Asia several thousand years ago. So big deal. The best estimate of people living in what is now called the USA was somewhere between 20-30 million. Maybe, if that. If someone challenges me on my native roots saying my ancestors came from Europe then the same argument goes to those who came here from Asia. There are 125 tribes in the US. None of them claim to be Native Americans. There were none until the Dept. of the Interior started classifying Americans. - the only country in the world to classify their own citizens.
Nobody is claiming 100M Indians in what is now USA. They're claiming 100M, which may be somewhat high, in all of North, Central and South America.
It is likely both Meso-American and the Inca Empire had at least 25M each, perhaps quite a few more. It is generally accepted, for instance, that the central valley of Mexico didn't get back to its pre-Cortez population till the 1950s.
In addition, it appears there were populous societies living in what is now the Amazon jungle.