Broad estimates of US war victims range up to 12 million (a liberal estimate), whereas the Nazis killed over 13 million through mass killings alone (eg the Holocaust + exterminated minorities). The Soviet Union alone lost 20 to 27 million depending on who you ask.
In addition to the 500k-millions of native peoples and hundreds of tribes the US systematically nearly eradicated, lets take just a few more examples.
- Vietnam: 1.5M killed
- Laos: 300k
- Iraq: 1M
- Indonesia: 500k-1M
- Korea: 500k
- Japan: 200k-1M in civilian bombings
And I haven't even started on operation condor and latin america yet.