It’s hard to quantify, but the US instigated or had a hand in causing most of the largest mass-killing events of the twentieth century.

To give just a single example, the CIA was the main driver behind the anti-communist massacres in Indonesia in 1965. 500k-1M people killed.

Or operation Condor, another anti-communist CIA-led program in several latin american countries: about 60-80k people killed, and 400k imprisoned.

A larger list of US atrocities is here.