"Sitting in the Smithsonian's National Museum of African American History and Culture is a rough cotton bag, called "Ashley's Sack," embroidered with just a handful of words that evoke a sweeping family story of loss and of love passed down through generations. In 1850s South Carolina, just before nine-year-old Ashley was sold, her mother, Rose, gave her a sack filled with just a few things as a token of her love. Decades later, Ashley's granddaughter,...