In 1492, when Columbus “discovered” America, the estimated number of Native Americans in what would become the United States was between 5 and 18 million.
Historians estimate that up to 80% of population loss was due to diseases like smallpox and influenza, to which the aboriginals had no immunity. A 20% survival rate of the lower estimate of 5 million would be 1 million; of the higher estimate, 3.6 million.
In 1900, the US Census showed a total Native American population of 350 thousand.
Which means that 65% to 90% of the populace is “unaccounted for”. Why do you think that is?