From Wikipedia :
American Civil War : Total 705,000–900,000 + dead
Chinese Civil War : 1.5 million + 250,000
From Wikipedia :
American Civil War : Total 705,000–900,000 + dead
Chinese Civil War : 1.5 million + 250,000
[0]: https://en.wikipedia.org/wiki/An_Lushan_Rebellion#Death_toll
The Russian Revolution is also nearly double the death toll.
One could also throw in the Wars of Religion and the 30 Years War as well.
It could easily be argued that earlier wars were either smaller, or not truly "civil" (because the rather pointless semantic distinction between internal and external wars has rarely been as clear as at the time and location of the American civil war).
Personally, I'd grant that title to the 30 years war (despite it's very international nature), but that is not because of any objective reasons, I just happen to live in a landscape culturally shaped by it.
Classic typo!