It would have been incomprehensible, at the turn of the nineteenth century, to believe that the actions of one man could set in motion a series of events that would reverberate through history for the next nine decades. Yet when Gavrilo Princip (1894-1918) stepped in front of the automobile carrying Archduke Franz Ferdinand and his wife, the Duchess Sophie, putting two bullets into their bodies and killing both, that is precisely the path on which he sent the world.

The son of a postal worker, Princip was born in Obljaj (Oblej), Bosnia. His father, Petar, was married late in life to a local woman, Maria, also known as Nana, who was fourteen years younger than her husband. Petar and Nana had a total of nine children, four daughters and five sons. Only three children survived infancy. Princip was the fourth child and second son, born seven years after...