Actually across two Americas (North and South) Some intentional, some as consequence of disease for which they had no resistance. The British gave the Arikara and the Mandan blankets they knew were infected with small pox. It annihilated both these tribes almost to extinction.

The US was guilty of an overt attempt at genocide with the War in the West (nits make lice policy). Many heinous massacres were perpetuate by European settlers on these shores of Native Americans. And this doesn't begin to cover what the Spanish did in Central and South America.

The only difference was the time frame. The Nazis did 6-8 million from 1933 to 1945. It took 200 years for the European invasion to work its toll.