While adding annotations for Reality Rules II, not only have I come across some great books, but I also have been dealing with a common cataloguer's dilemma: into which sub genre does a book fall? This is why we have editors, per se, and both Jack Batten and Russell Freedman's books about WWI are very good: Batten's book, The War to End All Wars: the Story of World War I, was a nominee for YALSA's 2010 Award of Excellence for Young Adults, and I wouldn't be at all surprised if Freedman's The War to End All Wars: World War One is a finalist for the 2011 list.
Should these books be entered in Defining Times? They were for Canada, perhaps not so much for the United States, and they would definitely fit in History's Darkest Hours, under Human Cruelties.
One I don't have any problem entering under that category, and another book I couldn't put down (and hadn't really wanted to pick up) was Dave Cullen's Columbine. The story of what really happened, and what went wrong in the tragedy and the aftermath as the survivors tried to pick up the pieces and the families of the slain fought for years to find out what happened despite the 'myths' perpetuated by the media and the investigators is presented by an investigator who has become the best authority on the subject.