How many armies in history have had the power to carry out mass murder on the scale of a million plus civilians in a single day, let alone planned to do so? Ki

How many armies in history have had the power to carry out mass murder on the scale of a million plus civilians in a single day, let alone planned to do so? Killing such a number of people in such a short time has been absolutely impractical until the last century. Only China, Japan, Russia, and the United States have been able to carry out such destruction and none have been able to do so in such a short period of time except for nuclear weapons in WWII.