That harks to the three kingdoms period where captured armies and populations were slain on the spot day and night day after day.

It’s reflected in their census figures: 56MM before the conflict period, 16MM after the conflict.

This is an often-popularized figure that the evidence doesn't really support (as much as I enjoyed Pinker's Better Angels, it bears a lot of the blame here). The "after" number is net of the loss of territory representing a quarter of the empire's territory, coincident with the breakdown of the census system, and post-removal of certain classes of people from being counted in the census. It's not a good proxy for lives lost during the course of the Rebellion. On top of that, the armies involved added up to a million people total, a tiny fraction of China's total population. As is almost always the case with large wars historically, the majority of deaths came from famine and disease caused by upheaval.

Surely the numbers are off but I think they are indicative and point to the utter ruthless methodical approach to decimation. One scene from a Chinese movie is etched into my mind. One of the executioners complains he can’t kill anymore because his blade had become too dull.