It's very interesting how there are always people who completely warp historical reality to suit their political agenda. I just now came across a bizarre claim by a Native American action group, claiming that European settlers in the USA (not the Americas as a whole, just the USA!) have historically killed 50 million Native Americans. And that's with disease not even included: they purely mean the purposeful killing of natives.
50 million. What a number! But a number out of thin air. The truth is that, after the Old World diseases had burned their way through the New World, there were only about 10 million Native Americans left in all of the Americas! Perhaps, if we're charitable, some 3 million of those lived in what is now the USA. How can you murder 50 million in a region where only 3 million exist? How could that be done? Do tell.
Either out of incompetence or out of wickedness, these 'activists' with their (too-)big claims are conflating certain numbers to fit their own narrative. The truth is that much larger numbers of Native Americans than those c. 10 million have indeed historically existed... but they died in vast multitudes due to disease. In all likelihood, Old World diseases killed c. 90% of the pre-contact population of the Americas. If the post-disease population is c. 10 million, that would make the pre-contact population c. 100 million.
Needless to say, there is a lot of debate about that. Historiographers once tended to consider numbers like 2 or 3 million when estimating how many Native Americans there must have been in 1491. But Henry F. Dobyns rather convincingly made the case for a number between 90 and 110 million, spread across the Americas.
Even the modern-day "low counters", who are sceptical of such high claims, simply believe that disease killed fewer people, like 50% for instance. (That's about the lowest credible estimate in use today.) So there are those who believe that disease killed 90% of the pre-contact population, leaving behind 10 million or so. And then there are those who believe disease killed perhaps 50%... leaving behind 10 million or so.
This is important to note, because this is where those 'activists' get it all wrong. In truth, the low counters simply believe there were much fewer pre-contact natives than the high counters do. That is the point of contention. But the 'activists' muddle the numbers. They claim the pre-contact numbers of the high counters (100 million) and the death rate of the low counters (50%) and claim that post-disease, there were some 50 million natives left.
That's simply not the case. And even then, that would be a number for all of the Americas, and not just for the USA.
Whether disease killed roughly 10 million or roughly 90 million or some number in between... that's still being debated.  But that there were roughly 10 million natives left in total after the disease had burned its way through the population is not under discussion.
Of those remaining 10 million, Europeans no doubt killed quite a lot. Although the fact that there are about 69 million Native Americans around today (which means considerable population increase from those 10 million), the amount killed by Europeans must not be overestimated. We are probably talking about hundreds of thousands. Probably not about multiple millions. Certainly not about tens of millions, which weren't there in any case.
 A footnote regarding the discussion about pre-contact numbers. Personally, I tend towards the position of the high counters. The effect of disease cannot be underestimated. By the accounts of Hernando de Soto (the conquistador, obviously, not the economist), who traveled the southeastern (later-to-be) USA in the 1500s, the place was filled with settlements. Hundreds of towns, from Florida to the Mississippi. When latter-day explorers reached the area again in the 1700s, they found... nothing. Except that De Soto had not made these villages up. Their archeological remains have been found. As have the mass graves that started appearing after he passed through.
The thing is, he brought livestock along, and animals escaped into the wild. They spread European disease, which killed countless natives and utterly destroyed many communities. This all happened without any Europeans there to witness or actively influence events. De Soto was gone when the dying started, and by the time other Europeans reached the area again, it was all over...