"At least 620,000 soldiers lost their lives from 1861 to 1865, constituting 2% of the American population. If the same percentage of Americans were to die in a war fought today, the number of American dead would be five and one half million." p.vii.
I got looking for WW II deaths and found this very interesting site. While the total number involved in WW II is staggering, as a percentage the death rate for the Civil War is a mind boggling 14.4%! Versus a still staggering 2.5% for WWII.