Faded ink. Inconsistencies. Fires. The deadliest conflict in American history, the Civil War, also had some of its worst-kept records, making the true number of casualties seem forever elusive.

For decades, historians have cobbled together clues. But thanks to a newly released set of census records spanning three decades, researchers have landed on a firmer estimate of lives lost: 698,000.

The analysis, published this week in The Proceedings of the National Academy of Sciences, also suggested that the Confederate states fared much worse than the Union, with a mortality rate more than twice as high. The granular nature of the census data means that researchers who build upon the work will be able to better understand the long-term impact of the war in the hardest-hit regions.

Caroline Janney, a history professor at the University of Virginia who was not involved in the research, said that she was intrigued by the census-based methodology and excited that the state-by-state data is likely to have other rich information, such as migration patterns among the newly freed population.

But she warned against interpreting modern social and political dynamics too readily through the lens of the Confederate death toll.

“There’s a reason that it’s still with us, there’s a reason that the memory still lingers,” she said. “Those deaths very much did shape their respective societies, but in a far more complicated and nuanced way than sheer numbers can represent.”