If it's a question of "[competing] with the most vicious regimes in history how cruelly one can treat one's opponents", then the US lost very badly to Japan. "

If it's a question of "[competing] with the most vicious regimes in history how cruelly one can treat one's opponents", then the US lost very badly to Japan. "As can be seen, nearly one out of every one-hundred people controlled by Japan [between 1937 and 1945] was murdered, or almost three per thousand people per year." (https://www.hawaii.edu/powerkills/SOD.CHAP3.HTM https://www.hawaii.edu/powerkills/SOD.CHAP3.HTM)