Not to pick, but that number includes CSA dead who cannot reasonably be said to have fought forfor the abolition of slavery.
Roughly 360K Union and 285K CSA make up the total, which has been revised upwards recently to closer to one million.
Not to pick, but slavery is NOT the only reason the Civil War was fought: invasion of their homelands, a terrible tariff on the South, states' rights, and, yes, slavery, etc.
A terrible price to pay, especially in the South that is being ignored by our modern day historically stupid media.