Isabel Wilkerson’s Caste:  The origins of our discontents, is a hard book.  Her words confront us with a hard truth about human behavior:  that humans are capable of imposing extreme cruelty and suffering on other humans and have done so at many points in history.  With brilliant writing and thorough research on three caste systems–American slavery and its aftermath, Nazi Germany, and the millennia-long caste system of India–she traces the forces that drive human behavior to destructive extremes.