Randolph Roth's American Homicide (Harvard University Press) is a wonky, meticulously researched, fascinating survey of murder in America that explores why we've become the bloodiest developed country on the planet. Roth, a sociologist and historian at Ohio State University, walks his readers from colonial times to the 21st century, all the while documenting, analyzing, and hypothesizing about why, how, and how often Americans kill one another.
Roth concludes that four factors contribute to fluctuations in the U.S. murder rate: political instability, a loss of government legitimacy, a loss of a feeling of belonging among outcast and historically oppressed groups, and a loss of faith in the social hierarchy. Crudely summarized, when Americans believe we're being governed wisely, fairly, equitably, and legitimately, we're peaceful and productive. When the government misbehaves, the citizenry tends to do the same.