Recent comments from modern historians have said that number is too conservative and the true total is probably closer to 3/4 million.
CC
K.I.A. -- killed in action (215,000) is a much smaller number than "died as a result of the war", which includes every manor of war related deaths, from illnesses to injuries which didn't kill outright, but shortened lives significantly.
Indeed, it is sometimes claimed that the Civil War "killed millions" -- claims supported only by noting a significant slowing in the rate of growth of US population during that decade.
With men away at war, fewer babies were born, more died in fancy, more older people died sooner from lack of care, etc., etc.