The population of Indigenous Americans is estimated to have decreased from approximately 145 million to around 10 million.
135 million.
Not all of that was the US, the old empires of France and Spain and England played a huge role, but since it’s founding the US has killed millions along with Canada and Mexico. Disease played a large role, but much of that was deliberately spread which muddies the estimates.
And that’s just one of the genocides the US was involved in. There have been many others.