[lmickh]

This is a common mistake when reading about military history. Casualties are not deaths. It is the lose of fighters for a wide range of reasons (death, injury, illness, catpure, and etc).

Roughly 650k people were killed during the American Civil War, but the casualties were closer to 1.8mil.

Much of the casualty count of the Franco-Prussian War is related to the fact that France lost entire forces in engagements. Mass routes nearly always lead to inflated injury and captured counts which in turn leads to high casualties.

By comparison, few of the engagements were as one-sided in the American Civil War. The combat death rates were actually fairly close to each other over time (~160k/yr).