For "Old Plantation Days: Being Recollections of Southern Life Before the Civil War" by Nancy Bostick De Saussure, the most fitting BISAC (Book Industry Standards and Communications) category would be "HISTORY / United States / Civil War Period (1850-1877)." This category encompasses works that delve into the era surrounding the Civil War, including personal narratives and recollections that provide insights into daily life, societal norms, and the social fabric of the time. Given the book's focus on recounting life in the Southern United States before the outbreak of the Civil War, this classification helps to situate it within a broader historical context for readers and researchers interested in the period.