America's most devastating war was far deadlier than textbooks say, according to a historian whose conclusions are finding support among experts.

The true death toll was probably about 750,000 - 20 percent higher than the traditionally quoted figure of 620,000 - and might have been as high as 850,000, according to J. David Hacker of New York's Binghamton University.

Even the old figure exceeded the combinted U.S. death toll of all conflicts from the American Revolution through the Korean War.

Hacker's conclusions, published in the December issue of the journal Civil War History, are "already gaining acceptance from scholars," the New York Times reported today.

The journal called the article "among the most consequential pieces" it has ever published, and Columbia historian Eric Foner told the Times the study "further elevates the significance of the Civil War" and "helps you understand, particularly in the South with a much smaller population, what a devastating experience this was."

"I have always been convinced that the consensus figure of 620,000 is too low, and especially that the figure of 260,000 Confederate dead is definitely too low," said Pulitzer Prize-winning historian James McPherson, according to a news release from the university.

The old estimate assumed similar death rates from disease for Union and Confederate soldiers, even though the North probably had better medical care.

Hacker arrived at his conclusions after studying improved census data released mostly in the last decade, the news release said.

After looking at reported male and female survival rates from 1850 to 1860, and from 1870 to 1880, he developed a baseline for typical death rates.

Then, looking at the data from 1870 - the Census after the war - he realized a lot more men were missing than the old death estimate could explain.

His new estimate suggested at least 650,000 died, and perhaps as many as 850,000.

"Roughly two out of three men who died in the war died from disease" - everything from diarrhea and measles to typhoid and malaria, Hacker said. "The war took men from all over the country and brought them all together into camps that became very filthy very quickly."

The range is wide because of several uncertainties, Hacker has admitted. After such a war, the next Census was understandably unreliable - a problem he tried to circumvent by comparing underreporting for both genders.

Also, there was no way to tease out the death toll for civilians, or pin down fatalities for each side, especially since men from border states fought on both sides.

The higher death toll also means tens of thousands more widows and orphans, Hacker pointed out to the Times.

Contact staff writer Peter Mucha at 215-854-4342 or pmucha@phillynews.com.