Dimitri Rotov asks what's happened to Edward Hagerman, author of The American Civil War and the Origin of Modern Warfare. I haven't read this book yet, but I've encountered it in footnotes often enough, especially in Hess and Nosworthy.
The answer seems to be that Hagerman isn't a Civil War historian, strictly speaking. He's an academic historian from York University in Toronto, and he's moved on to other military matters. His name is all over what looks like a massive left-wing conspiracy theory about alleged American biological warfare in the Korean War due to a book he co-authored in 1999, The United States and Biological Warfare. There's some suggestion that some of the key evidence that Hagerman and his co-author relied on in accusing the United States of waging biological warfare in Korea was most likely enemy propaganda.
Personally, reading the authors' unpublished reply to a negative New York Times review, it sounds to me as if they were neck deep in the Kool-Aid. Their key argument seems to be that Mao and Zhou believed that their troops were being bombed with anthrax, and why would they be lying in their own internal documents? I think the recent experience with Hussein's own people's belief that they had WMD, when they had not, and long experience with the endemic paranoia, myopia, and inclination to believe ones' own propaganda, characteristic of totalitarian governments, ought to make anyone careful about generalizing from the apparent beliefs of tyrants. When you throw into the mixture Kim Il Sung's well-known habit of manipulating his patrons and allies without compunction or restraint, and I can't imagine why you would ever want to rely on anything controversial coming out of that end of the historical record.
In short, I don't buy it, not a bit.