Always_Ask_Questions,
“not in absolute scale. Just the Napoleonic wars had 3M soldiers and 1-3M civilians killed…”
The Napoleonic wars lasted around 15 years, whereas the US Civil War was less than 5. In terms of scale (e.g., size of armies), they were not as far apart as you might think once the US and Confederate war efforts ramped up. Napoleonic tactics used during the Civil War had some rude awakenings with more modernized artillery and rifled muskets. Of course scale is relative, as neither of these conflicts can compare to the two World Wars. And even in the 19th century there were conflicts in China with a death toll an order of magnitude greater than the Napoleonic wars, e.g., the Taiping War, Dungan War.